The prosecution’s star witness — a forensics specialist named Herbert MacDonell — set out an array of props before the jury: a medicine dropper, a mirror hastily yanked from the wall of the courthouse bathroom and a vial of his own blood, drawn that day at a nearby hospital.

It was a strange sight in the 1985 Texas courtroom, and the jurors, the judge and even the defense attorneys watched, rapt, as MacDonell laid the mirror flat and then climbed up on a chair, holding the vial and dropper.

MacDonell’s expertise lay in an obscure discipline known as bloodstain-pattern analysis. He claimed he could reconstruct the events of a crime by reading the bloodstains left behind.

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Like a professor performing a classroom demonstration, he dipped the dropper’s tip into the blood and, with a practiced hand, released a single drop onto the mirror. It landed with a muted thud, forming a perfect crimson circle.

Blood landing on a flat surface should not spatter, MacDonell told the jurors with satisfaction. He let another drop fall onto the white shirt he was wearing. Blood lands differently on fabric, he showed them.

A defense attorney shot up from his chair in protest. This was a murder trial. There was no mirror at the crime scene. No medicine dropper. The demonstration was not reliable science, he argued. The judge disagreed.

MacDonell’s testimony would be pivotal to proving the Fort Bend County prosecutor’s theory that 21-year-old Reginald Lewis had murdered his family, shooting his mother and two brothers, and setting his father on fire. MacDonell had identified dozens of minuscule blood spots on Lewis’ clothing, and he said they placed Lewis at the scene during the crime

The jurors gave Lewis four 99-year sentences.

“MacDonell kind of took over the courtroom,” Lewis’ attorney, Donald Bankston, recalled, his disbelief still fresh. “It was almost like having Mr. Wizard.”

But MacDonell’s testimony that day did more than mesmerize the jury. It gave bloodstain-pattern analysis its first toehold of legitimacy in Texas courts, spreading it quietly, but surely, further into the justice system.

Two years later, Texas’ 1st Court of Appeals ordered a retrial because of evidentiary flaws (two retrials ended in hung juries), but it expressly rejected Lewis’ argument that bloodstain-pattern analysis was a “novel technique” that should never have been admitted and was not “scientifically recognized” or reliable.

“MacDonell’s studies are based on general principles of physics, chemistry, biology, and mathematics, and his methods use tools as widely recognized as the microscope; his techniques are neither untested nor unreliable,” Judge James F. Warren wrote for the court. To support his decision, Warren cited four other states — Tennessee, California, Illinois and Maine — that had already affirmed bloodstain-pattern analysis’ use at trial. Two of those states had based their decisions on court testimony by MacDonell.

A Texas court cited decisions from appellate courts in four other states — Tennessee, California, Illinois and Maine — to support its decision to allow blood-spatter testimony. Herbert MacDonell also acted as the expert witness in Illinois and Tennessee.

Warren’s hearty defense of MacDonell and his methods percolated through Texas’ courts, reassuring hundreds of the state’s judges that bloodstain-pattern analysis was reliable enough to be admitted at trial. They would allow it, again and again.

Over time, a parade of spatter experts, often trained by MacDonell — or by someone he trained — dazzled juries across the country with their promise of scientific surety, often tying bows of certainty on circumstantial evidence. Judges in Minnesota, Idaho and Michigan would rely on the Texas court’s decision when deciding to admit blood spatter in their own states in the 1990s. Those decisions, in turn, would be relied upon by other states.

Blood-spatter testimony spread through courtrooms across the country like a superbug.

Its path — the steady case-by-case, decision-by-decision acceptance of a new forensic science by the justice system — is one that’s rarely, if ever, been retraced. But it reveals the startling vulnerability of judges, and juries, to forensics techniques, both before, and after, they’ve been debunked.

Although the reliability of blood-spatter analysis was never proven or quantified, its steady admission by courts rarely wavered, even as the technique, along with other forensic sciences, began facing increasing scrutiny.

In 2009, a watershed report commissioned by the National Academy of Sciences cast doubt on the whole discipline, finding that “the uncertainties associated with bloodstain pattern analysis are enormous,” and that experts’ opinions were generally “more subjective than scientific.”

Still, judges continued allowing spatter experts to testify.

Subsequent research, funded by the Department of Justice, raised questions about experts’ methods and conclusions. But little changed.

All along, attorneys like Bankston continued challenging the admission of bloodstain-pattern analysts. But they came to learn that a forensic discipline, once unleashed in the system, cannot easily be recalled.

The Birthplace of Blood Spatter

About a four-hour drive northwest of New York City, down a quiet winding road, a house with bright red siding peeks through the trees, nondescript except for its fitting hue. At first glance, the home is typical. A side door opens into an overstuffed kitchen, where a stairwell descends to the lower level.

Down those steep stairs, in a sprawling warren of rooms, forensic history was launched more than a half century ago.

Modern American blood-spatter analysis didn’t originate in a federal crime laboratory or an academic research center. It started in Corning, New York, in MacDonell’s basement. Decades before blood-spatter analysis gained fame in TV series like “CSI: Crime Scene Investigation” or “Dexter,” MacDonell spent countless hours in his home laboratory, incubating and refining the technique.

Then, he spent a lifetime helping it spread.

MacDonell built his first basement laboratory in 1935, when he was 7, setting up some test tubes on a marble slab by the furnace in his childhood home.

But it wasn’t until the 1950s, when he was pursuing a graduate degree focusing on analytical chemistry, that he got a firsthand taste of real forensics while working in a Rhode Island state crime laboratory. After graduating, MacDonell took a stable job as a chemist for the local corporate giant Corning Glass Works, best known for its CorningWare casserole dishes. But in his off hours, he taught forensics at a nearby community college and began moonlighting as a consultant.

Pages from “Laboratory Manual for the Geometric Interpretation of Human Bloodstain Evidence,” an instructional manual written by MacDonell.

In 1968, the focus of MacDonell’s career began to narrow when he testified for a defendant in a New York murder trial. Steven Shaff, a veterinarian, had shot a former employee but claimed it was an accident. The prosecution said the man was sitting in his car when Shaff shot him. Shaff said the victim had thrown open the car door and knocked the muzzle of Shaff’s gun, discharging it accidentally.

When MacDonell studied the crime scene, he found blood spattered along the inside edge of the car door — an area only exposed when the door was open. It was proof, MacDonell testified, that Shaff’s story was true. The jury still found Shaff guilty of manslaughter. MacDonell was disappointed, but the case was a revelation: He could decipher a crime through blood left behind — and it whetted his appetite for more.

A year later, MacDonell successfully applied for a Department of Justice grant to continue his study of bloodstains. In 1971, the DOJ published his findings in a report titled “Flight Characteristics and Stain Patterns of Human Blood.” It would come to be known as the founding text of modern American bloodstain-pattern analysis, and its author, the pre-eminent expert.

MacDonell described blood spatters as a long-overlooked well of information. With a trained eye and a “natural scientific attitude,” he believed, investigators could analyze bloodstains at crime scenes to determine critical evidence such as where the victim was standing during the bloodshed and the kinds of blows — punches, shots, stabbings — inflicted. He documented his work in pages and pages of photographs of blood spattering on different surfaces: neat circles on a plastic wall tile, sprawling splotches on a kitchen towel.

In his report, MacDonell openly acknowledged the accuracy of his methods could not be quantified. “Final conclusions should be considered from the legal viewpoint of ‘proof within a reasonable scientific certainty,’” he wrote in the introduction. “Little attempt has been made to express data in this report in a statistical manner.”

The uncertainty did not slow his momentum.

Propelled by the report’s publication, MacDonell traveled to conferences and industry meetings presenting his research. He piqued the interest of prosecutors, defense attorneys and police officers who heard him, then hired him. Satisfied customers spread the word of his unnerving, but seemingly useful techniques.

More pages from “Laboratory Manual for the Geometric Interpretation of Human Bloodstain Evidence.”

Soon MacDonell quit Corning Glass Works to work full time as an instructor and forensic expert for hire. He branded his unaccredited basement lab with an impressive title, “The Laboratory of Forensic Science,” and named himself its director. In time, MacDonell would testify and publish books and articles using this official-sounding moniker. Few realized the limited scale of the operation.

A grainy VHS recording of a 1980s TV appearance showed MacDonell in a pristine white lab coat speaking with casual confidence about his grisly specialty. “Herbert MacDonell says he doesn’t work at home,” a local TV reporter said, “but rather lives where he works.”

The cameras captured charts covering the laboratory walls and a battery of expensive-looking scientific equipment resting on white countertops. A sign reading “Evidence Do Not Remove” mostly obscured a pair of shoes in an open cardboard box. Differently shaped and sized bottles of chemicals filled the shelves along with a tiny, human-like skull.

In 1973, the Mississippi office of a DOJ-funded agency invited him to Jackson to spend a week teaching police officers how to analyze bloodstain patterns. MacDonell quickly realized police departments liked having their own in-house experts. “I must’ve got good reviews,” MacDonell recently recalled, “because they kept asking me, ‘Would I teach this for them?’”

He began crisscrossing the country teaching 40-hour “Bloodstain Evidence Institutes” to groups of mostly law enforcement officers who trekked from small towns like Estherville, Iowa; Gulfport, Mississippi; Appleton, Wisconsin; and Sanford, Florida, to attend his courses. Although MacDonell would emphasize his own scientific education when acting as an expert witness, his advertisements assured students there were “no minimum educational requirements to be accepted into the class.”

By 1982, MacDonell had taught 19 institutes in eight states (Mississippi, New York, Florida, Alabama, Indiana, Illinois, Louisiana and Colorado), turning out scores of newly minted blood-spatter experts. He also gave single-day seminars in Germany, Italy, England, Switzerland and Canada.

At the end of each course MacDonell administered an exam, handing out certificates to students who passed. He would eventually teach for 38 years and recalled only five students who failed.

Then, he expanded his offerings. He began teaching advanced courses to students who already passed his basic course. Graduates of his first advanced class formed a new professional society — the International Association of Bloodstain Pattern Analysts — in 1983. The following year, IABPA published the first issue of the Journal of Bloodstain Pattern Analysis. MacDonell was named IABPA’s sole “distinguished member” in honor of his contributions.

In the span of about a decade, MacDonell had created an industry in which he became the reigning expert.

MacDonell launched modern bloodstain-pattern analysis from his basement in Corning, New York, more than a half century ago. Next door to his office is the laboratory where he performed some of his analysis of blood spatters left at crime scenes. (Katie Campbell/ProPublica)

A Growing Fame in Courtrooms

As he forged legions of bloodstain-pattern experts, MacDonell’s star continued to rise. A steady stream of cases poured into the Laboratory of Forensic Science. With his help, a savant-like mythos developed around him.

In 1987, Corning’s local ABC news affiliate ran a three-part series about MacDonell. “Herbert MacDonell,” the first episode began, “has been described as an American Scotland Yard, all by himself.” It was a line straight from the back cover of “The Evidence Never Lies: The Casebook of a Modern Sherlock Holmes,” a highly flattering book MacDonell co-authored about himself. Interviewers and attorneys often compared him to Holmes. MacDonell happily leaned in to the image, adopting a curved pipe and deerstalker hat for the cover of a self-published book.

Old courtroom footage, collected on VHS tapes by MacDonell, documented the deference he was shown. At a coroner’s inquest, a coroner introduced MacDonell’s testimony by waving one of his books before the jury and saying, “We have not called another expert of your caliber because we don’t have another expert of your caliber that we know of.” The coroner provided autographed copies of MacDonell’s book as a “nice memento” for each juror.

Over time, MacDonell was called to testify in increasingly high-profile cases.

During the hugely publicized 1981 trial of Jean Harris, a private-school headmistress accused of killing her ex-lover, “Scarsdale Diet” creator Herman Tarnower, MacDonell provided dramatic testimony for the defense. Holding Tarnower’s spattered bedsheets up before the jury, he explained the choreography of Tarnower’s death from the blood left behind. Harris was, nevertheless, convicted.

In 1994, O.J. Simpson’s defense team hired MacDonell, in part to demonstrate that the notorious glove found at the murder scene did not shrink after being soaked in blood, a theory the prosecution suggested to explain its ill fit on Simpson’s hand. On the stand, MacDonell recounted how he’d placed an identical glove on a photocopier to record its size, then saturated it in blood drawn from his own arm. When the blood dried, he measured it again. The glove, he said, holding up ghoulish pictures for the jurors, had hardly shrunk at all.

Lead prosecutor Marcia Clark cross-examined MacDonell for three days about the glove and his other testimony. She questioned the scientific rigor of his methods, suggesting he had inflated his resume. Yet even these aspersions, cast on national TV, did not slow the acceptance of bloodstain-pattern analysis.

Along the way, MacDonell’s reputation for eccentricity also grew. In his books, he described shooting dogs to record the resulting spatter and drenching a female student’s hair in human blood then having her shake it around to photograph the patterns. For decades, MacDonell collected his own fingernail clippings, preserving and pressing them between glass slides to study their striations, developing expertise in a field he called “fingernail identification.”

These macabre experiments only added to his intrigue.

“He’s the kind of guy that likes to have an audience,” recalled Martin A. Sells, a former DA in Columbia County, Oregon, whose testimonial once appeared on advertisements for MacDonell’s institutes. “He likes impressing you. But I never had a single doubt in my mind that he knew what he was talking about.”

Judges, too, were impressed. They regularly allowed MacDonell to testify in their courtrooms, based on his expertise and the industry he himself had built.

Eventually, defense attorneys began appealing convictions that relied in part on MacDonell’s testimony. They argued that MacDonell and his field were unscientific. But appellate judges almost never agreed. Again, and again, they affirmed MacDonell’s right to testify as an expert. “His background and experience were formidable,” the Supreme Court of Tennessee wrote in 1982.

In time, MacDonell’s students, many of whom only had 40 hours of training, started testifying as experts, too. Then, the students of his students. They modeled their testimony after his. They invoked MacDonell’s name as evidence of their expertise. They borrowed his phrases, his descriptions, his experiments, to support their analysis. Judges borrowed the reasoning of other judges who had admitted MacDonell when they ruled to admit his students.

In this way, over time, MacDonell’s testimony laid the legal bedrock for a field whose roots hardly reached further than the lower level of his home.

Winning Over Judges

For a new forensic discipline to grab hold, it needs to get past the court system’s gatekeepers: the judges.

Trial judges can refuse to hear evidence they deem unreliable. At the appellate level, judges review decisions made at trial and can deem an individual expert unqualified or label a whole field unreliable, banishing it from trial courts below.

Around the turn of the last century, judges rejected precursors to modern bloodstain-pattern analysts. Mississippi’s Supreme Court and the California Court of Appeal both affirmed decisions to exclude blood-spatter experts — in 1880 and 1927, respectively — on the grounds that their analysis added nothing to the jury’s own common-sense inferences.

But courtroom attitudes shifted as MacDonell’s brand of expertise seeped in.

In 1957, California’s Supreme Court accepted blood-spatter testimony from Paul Kirk, a man MacDonell cited as an inspiration. Kirk, a professor of biochemistry and criminalistics at the University of California, Berkeley, had worked on the Manhattan Project and was an early practitioner of bloodstain-pattern analysis. The court wrote that Kirk’s “inferences required knowledge and experience beyond those of ordinary jurors.”

1957 1966 Some early appellate courts, including in Alaska and California, accepted bloodstain-pattern analysis as reliable enough to be admitted at trial, even before MacDonell published his report or started teaching.

Kirk became the technique’s first flag-bearer. Nine years later, he would use blood-spatter analysis to help exonerate Sam Sheppard, a doctor who had been convicted of killing his wife in a trial so aggressively covered by the news media that the U.S. Supreme Court condemned the “virulent publicity” surrounding it. That same year, the Alaska Supreme Court accepted bloodstain-pattern analysis.

Then came a lull. Kirk died a few years after the Sheppard trial. Appellate courts mostly stopped talking about bloodstain-pattern analysis. Then MacDonell came along.

In 1980, Iowa’s Supreme Court became the first to review MacDonell’s testimony. The judges didn’t examine the accuracy of his technique. Instead, they cited his “status as the leading expert in the field.” Finding his testimony reliable, they noted MacDonell’s discipline had “national training programs”; “national and state organizations for experts in the field”; “the holding of annual seminars” and “the existence of specialized publications.”

With seals of approval from some of the country’s highest courts, bloodstain-pattern analysis continued its spread.

It moved east, gaining acceptance in an Ohio court of appeal, where both the defense and prosecution presented blood-spatter experts. Then south, as Tennessee’s highest court affirmed a trial judge’s decision to admit MacDonell as an expert. “Mr. MacDonell’s testimony was clear, understandable, and accompanied by demonstrations to the jury,” the court wrote. “He obviously knew whereof he spoke.”

1980 1982 1982 Iowa’s Supreme Court was the first to give bloodstain-pattern analysis a seal of approval on the basis of MacDonell’s testimony. Soon after, the technique’s admission was affirmed by appellate courts in Ohio and Tennessee.

MacDonell’s students carried the technique west to Oklahoma and Illinois. When a defendant argued a police officer who studied with MacDonell did not have a sufficient understanding of science to testify as an expert, an appeal court in Illinois responded, “We again reject the defendant’s argument that this area of expertise requires substantial training in physics.”

In Minnesota, a court affirmed expert testimony that bloodstains could reveal whether a victim was crouching or standing; in Idaho, that the stains showed a victim was walking away when shot.

After a while, some judges facing the issue for the first time simply cited the decisions of their counterparts in other states.

Acceptance of bloodstain-pattern analysis became almost inevitable.

Throughout, a handful of judges expressed concern. In 1980, Judge Mark McCormick of Iowa’s Supreme Court singled out MacDonell in writing. “I am unable to agree,” he wrote, “that reliability of a novel scientific technique can be established solely on the basis of the success of its leading proponent in peddling his wares to consumers.”

Judge Stephen Bistline of Idaho’s Supreme Court, in a vehement dissent in 1991, wrote: “The danger presented by expert testimony interpreting blood-spatter evidence is that the prosecution is provided with an expert who appears to be able to reconstruct precisely what happened by looking at the blood left at the scene of a crime. However, a quick review of the ‘science’ relied upon by the expert suggests that we would be better off proving guilt beyond a reasonable doubt without the help of such experts.”

But the skeptics’ dissents and uneasiness could not contain the spread.

By 2004, a Texas Court of Appeal wrote: “Have any courts held blood spatter analysis to be invalid? The short answer is no.”

Over time, growing layers of legal precedent protected bloodstain-pattern analysis, allowing it to flourish unhindered.

1983 1984 1990 1991 MacDonell’s students testified about bloodstain-pattern analysis at trials in Oklahoma, Illinois and Idaho. When the testimony was challenged, appellate judges in those states found the analysis reliable enough to be admitted at trial. In Minnesota, a court found an expert qualified enough to present blood-spatter testimony, in part, because he had previously performed 30 to 35 blood-spatter interpretations in other cases.

Attorneys on both sides began presenting competing experts, assured they would be admitted. Some forensic scientists grew concerned by the number of police officers qualifying as experts based on a mere 40 hours of formal training.

MacDonell deflected responsibility in one of his books. “The fault for permitting such individuals to testify as an expert must rest with the opposing attorney,” he wrote, adding that “a judge should be able to recognize unqualified charlatans.”

MacDonell ran his last Bloodstain Evidence Institute in 2011. By then, he had taught 75 workshops and over 1,000 students. Some of them replicated his business model, running 40-hour workshops of their own. This new wave of blood-spatter entrepreneurs established fiefs in different corners of the country, advertising their services through the IABPA.

In 2012, MacDonell, then 84, retired. That same year, two girls alleged he had sexually abused them when they were 11 and 16. One said the abuse occurred while she was a student at a summer forensics program taught in his home. MacDonell was charged in Corning Town Court with forcible touching, two counts of endangering the welfare of a child, exposure of a person and aggravated harassment in the second degree. He pleaded guilty to the harassment and the remaining charges were dropped. MacDonell said recently that he’d done nothing wrong and pled to the charges on “the bad advice of my attorney.”

Afterward, no lawyer could reasonably present MacDonell at trial as he was too easy to undermine on the witness stand. His career as an expert witness was over.

But by that time, the field hardly noticed his absence. Others, many members of law enforcement who got their start as MacDonell’s students, had taken his place at the forefront of the discipline. And while the technique’s earliest experts, MacDonell and Kirk, had impressed judges with their extensive scientific backgrounds, many of the new wave of experts had little to no scientific education at all.

In 1880, the Supreme Court of Mississippi is the first to mention the use of blood spatter at trial. It will take another 77 years for the forensic discipline to begin gaining acceptance by the courts. In 1957, the Supreme Court of California is the first to accept bloodstain-pattern analysis as reliable enough to be admitted at trial. In 1973, Herbert MacDonell teaches his first 40-hour course on bloodstain-pattern analysis. Over the next 45 years, appellate courts in 36 more states decide that bloodstain-pattern analysis is reliable enough to be admitted at trial.

A Technique Puts Down Tenacious Roots

In 2006, federal Judge Nancy Gertner handed down a sentence that still haunts her.

A jury in her courtroom convicted a man named James Hebshie of burning down his convenience store to fraudulently collect insurance money. Gertner thought the prosecution’s most damning piece of evidence — that a state trooper’s accelerant-sniffing dog identified where Hebshie started the fire — was bogus. But Hebshie’s defense attorney never objected, even when Gertner interjected three times, offering him the chance.

Without arguments before her, Gertner could not exclude the evidence. The mandatory minimum sentence was 15 years, and she had to impose it. “I was appalled,” she said.

Before her 1994 appointment to the bench, Gertner worked for years as a defense attorney, scrutinizing and challenging forensic evidence presented against her clients. She later taught law students about the risks of forensics as a professor of evidence at Boston College Law School. But as a judge, she realized cases like Hebshie’s could render her powerless.

So, when the National Academy of Sciences’ groundbreaking report on forensics came out in 2009, Gertner saw an opportunity.

The report was a rigorous examination of the forensics widely used in the nation’s courts and revealed troubling inadequacies with virtually every technique. It included a harsh assessment of bloodstain-pattern analysis and questioned the abilities of experts in it. A capable analyst, it said, must possess an understanding of applied mathematics, significant figures, the physics of fluid transfer and the pathology of wounds — subjects that aren’t covered in depth in the field’s 40-hour workshops.

After the National Academy of Sciences published its critical report on forensics, Nancy Gertner, then a federal judge, tried to force more scrutiny of bloodstain-pattern analysis and other forensic sciences. But her colleagues didn’t follow her lead, which she deems “an institutional failure.” (Katie Campbell/ProPublica)

Using the National Academy of Sciences report as a launching pad, Gertner published instructions for attorneys arguing cases in her courtroom, the gist of which were: “If the evidence at issue is challenged in the NAS report, I will automatically hold a hearing.”

“If the courts routinely admit junk science,” Gertner said recently, “the lawyer with a finite amount of resources is not about to say I will spend this dollar on a challenge if it’s not going to make a difference.”

Other judges on the U.S. District Court for Massachusetts did not follow her lead. “Everybody thought I was crazy,” she recalled with a wistful laugh. Gertner was used to being an outsider. She was one of a few women litigating criminal cases in the 1970s. Among her judicial peers, defense attorneys were a rarity.

Still, she was disappointed to see how few judges — on the federal bench or in state courts where the majority of spatter cases arose — saw the National Academy of Sciences report as a call to action.

Gertner, who retired from the bench in 2011 and now teaches at Harvard Law School, said the failure of the report to take hold in courts “was an institutional failure.” Lawyers failed. Trial judges failed. Appellate judges failed.

She saved her strongest criticism for appellate judges who, she insisted, could raise the stakes of admitting bad science by shaming trial judges that do.

“If you were reversed by the court of appeals for allowing in junk science,” she said, speaking as a former trial judge, “you are bound to be more critical the next time you have this issue.” But appellate judges are loath to overturn forensic-related precedent, even in the face of advancing scientific understanding.

“Precedent is like a child’s game of telephone,” Gertner said. “You start off saying something. You whisper it down the line and you continue to whisper it even though it no longer makes sense.”

For attorneys, convincing appellate judges to break ranks has proven Sisyphean.

Last year, Geneva Williams, a defense attorney in Iowa, used the concerns raised in the National Academy of Sciences report to argue that her client’s former lawyer was ineffective for failing to challenge the admission of bloodstain evidence at his trial. Her client’s conviction, she said, should be overturned. The court rejected her argument.

“The admissibility of such evidence is determined by the Iowa Rules of Evidence,” Judge Richard Blane wrote for the Court of Appeals of Iowa, “not a research journal.”

The expert who testified at the trial was a former IABPA officer who studied with MacDonell.

Questioning the Real-World Value of Research

While the National Academy of Sciences report fell flat in the courts, its findings roused the Department of Justice. The department and other federal agencies began doling out millions to researchers to enhance the scientific bona fides of forensic disciplines like bloodstain-pattern analysis.

Starting in February 2010, the DOJ’s research arm, the National Institute of Justice, offered a pool of grant money for a study of the fluid dynamics of blood.

The call for proposals landed in the inbox of Daniel Attinger, a fluid dynamics specialist at Columbia University in New York. Attinger, who wears round, frameless glasses and sneakers with his suits, had been training computers to recognize fluid stains: first, to differentiate between Coke and Diet Coke, then between Cabernet and Merlot.

But “bloodstains,” he recalled thinking, “had more important stories to tell.” He just didn’t know anything about them.

So, Attinger read everything he could and then, like so many before him, made the trek to Corning, to learn from the man who had propagated the very technique the National Academy of Sciences report now questioned. He went to MacDonell’s house.

The two men huddled in MacDonell’s kitchen, talking about Attinger’s research ideas, MacDonell’s methods and the practical needs of investigators in the field. “What he knew, he was able to explain clearly,” Attinger said of MacDonell. “He also had a clear understanding of what he did not know.” In the unknowns, Attinger saw potential.

That summer, Attinger attended one of MacDonell’s final 40-hour workshops. By fall, Attinger’s team won a grant of just over $632,000 from the DOJ to start their studies.

In 2013, Attinger published his first blood-spatter paper in the journal Forensic Science International. One of his three co-authors was a now-retired Canadian police officer who had been an assistant teacher in MacDonell’s workshop.

The paper showed that the hypotheses that underpin bloodstain-pattern analysis remained largely untested. And, it said, analysts’ assumptions and errors could make their conclusions rife with uncertainty. Analysts failed to properly account for gravity when using bloodstains to calculate victims’ locations. They assumed things about how speed influences blood patterns that had never been scientifically proven.

But Attinger’s paper had a solution: It posited fluid dynamics research as a promising way to refine the accuracy of bloodstain-pattern analysis.

Once published, the article didn’t attract widespread concern, but it did attract more funding.

Today, Attinger, now at Iowa State University, has been studying the technique for eight years and has received over $1.3 million in federal grants. Other scientists have received grants, too. The NIJ alone dedicated $175 million to forensic research between 2009 and 2017.

A review of Attinger’s research reveals some investigation of fundamental questions, like trajectories of blood in flight. But his experiments are highly simplified and extremely specific when compared with the complex problems faced at crime scenes. “The key in doing meaningful experiments,” he said, “is to start from the simple, understand it and then go to the complex.” A recent paper, for example, examined distortions of bloodstains on perfectly flat-lying military fabrics, results that Attinger and his co-authors said could be generalized to any woven fabric that had been laundered four or more times.

Such studies frustrate forensic experts like Ralph Ristenbatt, an instructor of forensic science at Pennsylvania State University and 15-year veteran of the Office of Chief Medical Examiner in New York City. “These are great academic studies,” he said, “but what do they lend to real-world problems?” Ristenbatt said he isn’t sure researchers will ever be able to model lab experiments as complex as real life, so they may not be the best way to address the chasm between analysts’ training and the conclusions they draw at crime scenes.

“There’s this belief out there that you can look at the patterns of blood at a crime scene and it’s the be-all end-all,” he said, “when in reality bloodstain-pattern analysis is just one tool in the toolbox of what we call crime-scene reconstruction.” The very idea that bloodstains will “tell the story for us,” he said, is “misguided.”

At a shooting range in Ames, Iowa, Attinger and his colleagues study how gunshots generate blood drops by using lasers and high-speed cameras to create 3D images of the moments after a bullet hits a blood-filled target. They collect the spatter stains on tagboard with pieces of T-shirt and camouflage fatigues as part of a U.S. Army-funded research project on blood stains on military fabrics. (Katie Campbell/ProPublica, and Greg Davis, special to ProPublica)

Attinger freely admitted that his years of work have had little impact on practices of blood-spatter experts at crime scenes. “I would say there’s been no change,” he said. But he saw no reason for law enforcement to hit pause until techniques improve.

“I have trust in the U.S. justice system,” he said. The technique’s limitations, he said, “are known by both the prosecution, the defense and, hopefully, the judge.”

Attinger now appears to be a part of the very industry he was hired to scrutinize.

In 2015, he co-taught an advanced bloodstain-pattern analysis course to members of the Las Vegas Metropolitan Police Department. His partner was Craig Moore, the retired officer who co-authored his first blood-spatter article. Attinger taught an introduction to ballistics and the fluid dynamics of blood-stain pattern analysis, while Moore taught the practical application of the discipline. “An advanced class is designed for a person who will be testifying in court,” Moore said. Attinger said he had “no opinion” as to whether the students were qualified to act as expert witnesses after completing the course.

He is also a dues-paying member of IABPA. In June, Attinger spoke at the first South American IABPA conference. “A whole continent is eager to do #forensics with bloodstain patterns,” he tweeted afterward. “Go for it!”

One month later, Attinger settled a lawsuit with Iowa State University, whom he had sued after student complaints about verbally abusive conduct led to an internal investigation and sanctions against him. He claimed the process violated school policy and his constitutional rights. Attinger denied the allegations, saying he is “very articulate and honest in the feedback” he provides to students. “Some people do not like to receive honest feedback and not everyone is called to be a researcher.”

The settlement allowed Attinger to remain at Iowa State and work full time on research and related activities, but only until 2021 when a current grant expires.

Today, Attinger talks a lot about his new idea: He’d like to develop a computerized, handheld device that analysts could use to read bloodstains at crime scenes — even if they didn’t understand the complex science behind them.

Ristenbatt said the justice system would be better served by more educated investigators who could grasp the limitations of different forensic techniques. Ristenbatt also used to teach introductory blood-spatter courses, but said he stopped when he realized his students were holding themselves out as experts. “The easiest way to control it, is not to do it anymore,” he said.

In 2016, the Texas Forensic Science Commission — a state panel consisting of seven scientists, one prosecutor and one defense attorney — opened an inquiry into two cases that turned on bloodstain-pattern analysis. At the center of one is Joe Bryan, a beloved high school principal who has been in prison for 31 years over the killing of his wife. The bloodstain-pattern analyst in that case, a local police officer who took a 40-hour class with one of MacDonell’s former students, recently acknowledged that his conclusions were wrong.

Ristenbatt gave an impassioned speech to the commission, calling for mandatory educational requirements for analysts, including a four-year degree in natural or forensic science. In February, the commission announced it would require accreditation for all bloodstain-pattern analysts testifying in court starting in May 2019. Commission decisions only affect Texas courts, but have influence across the country.

In the meantime, experts in the old methods — the ones that got their start all those years ago in Corning — keep testifying.

“I think if you were to do a study,” Ristenbatt said in an email, “of all the people who call themselves bloodstain-pattern experts and you looked at the genealogy, if you will, of how they’ve obtained their training, it’ll all likely come back to Herb MacDonell through some means.”

“I Am Very Satisfied”

MacDonell still lives in the big red house in Corning. He is 90 and uses a stair lift to descend to his laboratory. It takes, he said with characteristic precision, exactly 31 seconds to reach the last step.

The stairs lead to a long hallway lined, floor to ceiling, with fading photographs of MacDonell’s students, their changing hair styles and glasses a vivid timeline of his decades of teaching.

The laboratory now has the fluorescent-lit feel of a high school chemistry classroom. The rows of bottles, still there, are covered in layers of dust. The whole room has a yellowed tint to it, like stepping into one of the old photographs on the wall.

Behind the lab, in a large office, MacDonell carefully catalogs his legacy. A thick book details every student who attended a Bloodstain Evidence Institute. A glass display case showcases mementos from police departments across the country. Stacks of VHS tapes chronicle courtroom triumphs and TV appearances.

MacDonell, now 90, reflects on his role in spreading bloodstain-pattern analysis throughout the country. (Katie Campbell/ProPublica)

Today, MacDonell’s demeanor is much the same as it was in his earliest videos. He is confident, sometimes curt. Little gets under his skin as much as people who refer to his field as “blood splatter” instead of “blood spatter,” a phrase he said he coined (“Splatter is splash. Spatter is not splash,” he said). He is keenly aware of his impact.

“Overall,” MacDonell said, “I am very satisfied with my life’s accomplishments and have few regrets.”

When asked to pinpoint the proudest moment of his long career, MacDonell’s answer comes easily: Susie Mowbray’s exoneration. Mowbray was imprisoned for nine years over the killing of her husband. At her retrial, MacDonell used blood spatters to reconstruct the crime, testifying her husband’s death was a suicide and discrediting the expert who testified for the prosecution at her first trial. The expert was MacDonell’s former student.

MacDonell has testified against his own students numerous times. Asked recently whether he ever considered changing his course structure, or certification process, after seeing students give faulty testimony, MacDonell answered in the negative. “You can’t control someone else’s thinking,” he said. “The only thing you can do is go in and testify to the contrary.”

Leave it to the lawyers to cross examine, to the trial judges to exclude, to the appellate judges to overturn.

According to MacDonell, this June marked 50 years since he first testified about blood-spatter analysis. To honor the occasion, he planned to pour himself a glass of single-malt scotch and toast Shaff, the client whose case unleashed modern American bloodstain-pattern analysis on the world. Sitting in a home maintained as a shrine to his accomplishments, MacDonell could rest assured, his legacy would be protected in the courts for years to come.

Leora Smith was a senior research fellow at ProPublica. She graduated from Harvard Law School in May 2017. Leora has worked with and provided legal support to the Bronx Defenders, the Service Employees International Union, Amnesty International Canada and other international human rights organizations. Her work can be found on the labor law blog On Labor, The Canadian Broadcasting Corporation’s "The Fifth Estate" and in the Harvard Civil Rights-Civil Liberties Law Review.