“New murder case,” read the note that the criminalist jotted in his journal on August 24, 1925. He slipped a white lab coat over his dark suit, settled into his chair, and slid over a microscope. Now he was forced to look at the clue once again, fully examine it—a horrid task, even for a trained investigator. In many murder cases, Oscar found that either the killer or the victim would seem fascinating to him. In this case, it would be both.

The sky had darkened outside as Oscar snapped rubber laboratory gloves over his hands. The Berkeley Hills neighborhood was virtually silent at night after families flicked off their lights, but inside his cavernous lab, Oscar prepared to solve a dreadful case involving an enigmatic victim who would trouble him for the rest of his career.

The criminalist stared down at the brown object that the boy had discovered the day before in the tule swamp of El Cerrito. A dainty, delicate ear slid from his sanitized container and landed on a sheet of white construction paper. He squinted at the matted light brown hair—the ear was attached to part of the scalp. It rested there on his desk like a trinket sent by a macabre admirer. Oscar leaned toward it, adjusting his spectacles.

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A dainty, delicate ear slid from his sanitized container and landed on a sheet of white construction paper.

The ear’s exterior was covered with small light freckles, likely from years of sun damage. He noted the ear’s size and shape. There was a tiny hole in the lobe for an earring—detectives had missed that detail. So this was likely a woman’s ear. Oscar placed her scalp on some paper with a grid and reached for his measuring tape. He scribbled down some numbers and gently lifted sections of her hair—no evidence of blood clotting.

“Cut after death,” he wrote. “Dismembered.”

But why? Oscar knew that many times a killer dismembered his victim to prevent identification. Maybe he knew her? Searchers found another segment of scalp nearby, wrapped in a month-old newspaper. Investigators were canvassing the neighborhoods near the swamp, hoping to find witnesses.

Detectives entered every duck blind and hunting lodge along the shores of San Francisco Bay and tiptoed along the edge of the swamp where they discovered some women’s clothing that had been cut into small pieces and wrapped in Oakland newspapers.

Oscar sensed urgency from investigators because the bloodthirsty media would soon pick up on the story; the violent tale of a depraved killer would surely frighten all of El Cerrito.

In his lab Oscar picked up a hatchet laying on his table, a sharp weapon discovered inside a cottage a half mile from the swamp. The owner claimed she hadn’t stayed there for more than two weeks; she said she had been rattled by the crimson spots on the blade.

“I do not know how blood stains got on to it, for I have not killed chickens, rabbits, or anything else,” said Iva Graham. “How blood got on to it, as the police say, is a puzzle to me.”

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Oscar fingered a small bottle filled with clear liquid and “benzidine” written on the side. Using an eye dropper, he dribbled it onto the edge of the hatchet and waited for the red liquid to turn blue, signaling blood. Nothing. Even if the killer had hidden inside the cottage, he hadn’t used the weapon on his victim.

Oscar worked for nearly twelve hours inside his lab that day, assembling a composite profile of the victim: a woman in her twenties, naturally blond with hints of red and brown, a lady of some refinement because of the high-quality texture of her hair and skin. Oscar could tell that she took pride in her appearance. She was of Scandinavian descent, he suspected. Based on the wound, he estimated that she had died a week earlier.

A knock came on his laboratory’s door, and standing in the doorway was Contra Costa County sheriff Richard Veale, who had been the lead investigator on Charles Schwartz’s case weeks earlier. Oscar smiled. He and Veale had communicated well on that case, and now they would be working together again. August Vollmer also sent Captain Clarence Lee, the cop who had chatted with Charles Schwartz as he secretly pondered how to commit the perfect murder. Oscar frequently worked with the same investigators, especially in cities much smaller than Los Angeles or San Francisco. Berkeley boasted a strong cache of detectives, thanks to Vollmer, but there were just a few who could be trusted with major crimes. These were two of his favorite cops. Oscar wondered to himself: Who was this woman, and where was the rest of her body?

With metal tweezers, the forensic scientist retrieved several fly larvae, which he found developing in the fatty tissues underneath her ear. These tiny insects would help him estimate her time of death. He flipped open The Control of House Flies by the Maggot Track, a short book he had received seven years earlier from John Boynton Kaiser. The reference librarian delighted in new scientific techniques and realized that the book might help Oscar determine the time of death using bugs.

The study of insects in crime solving, known as forensic entomology, had been used since the mid-1800s by a handful of scientists in Europe who hoped to use nature as a co-investigator, but the method had never been documented in a criminal investigation in America—this case would be the first.

There are two primary ways to determine time of death, or postmortem index (PMI), using insects. The first is to use the secessional wave of bugs. In Kaiser’s book, Oscar read that Calliphoridae (known as blowflies) typically are the earliest of all insects to respond to a decomposing body; much of the time they lay their eggs on the corpse within twenty-four hours. Other species, like beetles, arrive only after advanced decomposition. Oscar found only blowflies on her ear, signaling that she had been recently killed. He was relieved—the longer a body was missing, the harder it would be to find . . . and Oscar desperately wanted to find the rest of this woman.

He also used a second method in forensic entomology, which was to measure the larvae’s age and development, their relative age. These insects were in their earliest stage, so the murder was recent, perhaps within forty-eight to seventy-two hours before he had received the ear in his lab. It was a remarkable claim that few criminalists at the time could have made. And then Oscar entered the mind of the killer, the only way he could discover who would have dismembered a body and then hid its pieces.

“Assuming an additional twenty-four hours to be required to prepare the body and clothing fragments for distribution,” he wrote, “I estimate the time of death as approximately ninety-six hours before the afternoon of August 24th.”

Oscar had to narrow down that timeline even more. If someone had just killed someone and wanted to dismember her body, he thought, it could take quite a long time. When might he have the most time to work undetected? The darkest night of the week. Oscar flipped through a local newspaper until he found a table of tide and moon phases over the past few days.

“The murder and distribution could be performed unobserved at any time after 8:30pm of August 19th, 20, 21, and 22,” Oscar wrote.

Within twelve hours of being handed just one dreadful clue from the swamp, Oscar had created a profile of the victim and then estimated when she had been murdered. Now police tasked him with directing them to the rest of her body. He picked up the clothing found in the neighborhood near the swamp, a brown jacket with a fur collar that likely belonged to the woman. Using a magnifying glass, he discovered wet sand throughout the fabric, a key clue. He turned to a reliable tool, one of his most favorite. He slid his chair over to the petrographic microscope, the same one he had used in Father Heslin’s case four years earlier. “Small fragments of plaster, coal, decayed redwood and similar debris which leads me to believe that burial of the clothing during temporary concealment of it was under a house,” Oscar noted.

He was coming closer to finding her. The sand was his best clue, evidence that might lead police to her body. And now the press was adding to his strain.

He was coming closer to finding her. The sand was his best clue, evidence that might lead police to her body.

“Tule Swamp Drained to Find Body,” one headline read. When reporters realized that “America’s Sherlock Holmes” was working the case, they hounded him for details—he ignored them all. Oscar was still sorting out his relationship with the press, which was shaky and even hostile after years of inaccurate reporting and unflattering profiles.

“The city editor is, without exception, a spud-bug and a road-hog on news,” he complained to John Boynton Kaiser about one newspaperman, “and his reporters scurry around like a nest of road lice getting it in . . . ready on the instant to apply the powerful screws of the great press they represent, like cockroaches.”

Oscar cooperated with a select number of reporters, and he often praised papers like the San Francisco Chronicle for being judicious with their crime coverage. But he was still suspicious of the media even when he was at the center of a case with a favorable outcome, like the Siskiyou train robbery, and he viewed the press as a tool, not an ally.

“Because of the higher presence under which they work, their chestiness over their jobs, their intense rivalries,” he wrote Kaiser, “their suspiciousness, their cynicism, they require careful handling.”

Ironically, Oscar didn’t seem to realize that he was facing those same challenges with his own professional competitors, the forensic experts who were his antagonists during dramas that would be on display in American courtrooms for the next two decades.

***

Oscar revealed bits and pieces of new evidence, and investigators snatched each one to feed to the press. The sand from the victim’s clothing contained small particles of clamshells. There were enough shells to suspect that the sand originated near the ocean, but not enough to have come from a seaside beach.

Oscar stared at the grains. What type of water was near an ocean in this part of Northern California? There was no sand hidden within the tule stalks of El Cerrito, just black muck. He pushed his microscope to the side and grinned.

“Size of rock particles indicate alternate current and periods of quiet with deposit of water borne material,” Oscar wrote. “Suggest backwaters of stream emptying into tidal waters.”

The sand did not come from the nearby beach in El Cerrito. It came from water that flowed into the ocean; Oscar was certain. He dug into a drawer and pulled out a United States Geological Survey map, a document that would show the regions where that type of sand might be found. He studied it, shifting his eyes back and forth between one particular location and El Cerrito. It seemed too unbelievable to be true. He circled one area with a pencil and then braced for dozens of questions from hesitant detectives.

“It’s somewhere around Bay Farm Island,” Oscar told them. They stared back.

“That’s fully twelve miles from El Cerrito, where we found all this,” one of the detectives argued. “It’s even in another county.”

Oscar’s explanation was slow, thorough, and confounding to the investigators. He described the results from his petrographic test—the woman’s clothes contained just a tiny amount of salt and chloride (like ocean sand) but quite a lot of freshwater vegetable matter and chemicals—like sand from a bog. The detectives seemed to follow his logic.

“From the size of these grains of sand I determined that they came from a spot where there were fresh-water gullies and where the movement of the water over the land was slow,” he explained.

The sand came from slow-moving water, and that’s what he wanted to find on his geological survey map—that spot.

“The most likely place was Bay Farm Island,” Oscar explained. “The island is separated by Alameda by a slough and into this the fresh water of San Leandro Creek flows. That accounts for the fresh water element I’ve talked about and would provide conditions to produce sand similar to that which I found.”

Oscar didn’t know it yet, but his methods would make forensics history once again. He had used yet-unpublished methods of discovering quartz grain surface textures to point police toward a new location. It’s a technique used now by modern forensic geologists, but Oscar didn’t have the benefit of using today’s atomic force microscopes.

Those devices create high-resolution 3-D images using a small probe with a sharp tip that scans back and forth across a grain of sand to measure the surface topography at up to atomic resolution. Instead of using a spacial database on a computer to chart the body’s coordinates, as current researchers might, Oscar used his geological map and plotted out the origin of the sand—a remarkable technique. The detectives looked at each other. Oscar Heinrich was rarely wrong, they concluded. The men prepared to issue new orders to the searchers.

If El Cerrito was a lush marsh, Bay Island Farm was a muddy bog. Police and volunteers slipped and slid along the mudflats under the drawbridge, hauling shovels and spades with the intention of unearthing a corpse.

Newspapers printed Oscar’s description in their headlines: “Victim Young, and Woman of Refinement, Experts Declare after an Inspection of Clues.” Police desperately searched for the identity of the young, blond, well-kept woman of Scandinavian decent. And in less than twenty-four hours, they would find her.

***

The forensic scientist had spent the last few years admiring his sons as they studied in the rooms above his lab on Oxford Street. One boy could be found with his nose in a book, while the other seemed to prefer daydreaming. Oscar’s assessment of their future would shape their lives, to a certain extent. One son would feel immense pressure to equal his father’s success, while the other would struggle throughout his youth to satisfy his father’s high expectations. Theodore, who was fifteen years old in 1925, mimicked Oscar in most ways.

“He is well balanced, quiet, courteous, and helpful,” Oscar proudly told his mother before she died. “In every respect he is a very agreeable boy to have around. For a young boy he has an unusual range of expression and quite an ability to write.”

But eleven-year-old Mortimer served as a sort of friendly foil to his older brother.

“Mortimer persists in being the opposite of Theodore,” wrote Oscar. “He is quick at learning, but it is somewhat hard to keep him at it.”

The complicated relationship between Oscar and Theodore, as they both aged, would impact the criminalist’s life. But he adored his eldest son.

“My dear big boy,” Oscar wrote Theo on his fifteenth birthday. “Your birthday brings to me pride in your growth to new duties and responsibilities and fond recollections of your very earliest days with your mother and I.”

Oscar’s interests away from his lab continued to multiply. Despite a blunt rejection from one fiction editor in New York, he had not abandoned the idea of publishing a detective story. He moved on to another publisher, vowing to never give up—his mantra in life.

“The book which you remember and concerning which you have so kindly inquired is not yet written,” Oscar wrote a friend. “There never has been any difficulty about a publisher for it. In fact, Appleton is waiting for something from me now.”

Crafting stories to both titillate and educate readers would motivate him to carry on at his writing desk. He seemed to hope to die with a pen in his hand, not a magnifying glass.

“As you know,” Oscar wrote to his friend, “writing maketh an exact man.”

It would be decades before he would learn whether that fantasy would become real.

***

Her tibia lay next to her fibula. A measuring tape stretched out alongside her humerus, her upper arm. It was easy to lose count of so many tiny bones. She had been scattered across the mudflats of Bay Farm Island, precisely where Oscar Heinrich predicted she would be found, about twelve miles from El Cerrito.

Two searchers carrying shovels found the skull pieces buried beneath a drawbridge by a river. Small clamshells adhered to her bones. When Oscar received the evidence at his lab, he felt satisfied, even relieved. Once again, his unique methods worked, separating him from the lesser investigators who claimed to be his peers. No one else could have accomplished this, he crowed to himself. Oscar removed his tweed jacket, rolled up the sleeves of his white dress shirt, and snapped on his dark rubber gloves once again.

Her tibia lay next to her fibula. A measuring tape stretched out alongside her humerus, her upper arm. It was easy to lose count of so many tiny bones.

“Examined a skull which has been cut in several fragments with a saw and cast into the waters of San Francisco Bay from the Bridge leading to Bay Farm Island,” Oscar wrote. “Killed by a blow on the top of the head with a blunt instrument and thereafter her body was dismembered and cut up into small units and these units distributed over Alameda and Contra Costa County.”

Oscar slid her upper and lower jawbones in place, completing the skull. Her head faced toward the ceiling with her jaws wide open, as if she was killed in mid-scream. A pair of schoolboys unearthed a bag containing her kneecaps, ribs, and other bones, meaning that someone had tried to remove her flesh using chemicals. The killer also buried a large piece of her torso under the bridge on Bay Farm Island, along with a lung. Police found a piece of a woman’s breast and her abdomen in Rodeo, thirty miles north. The El Cerrito marsh where the scalp was found was about halfway between the two locations.

“It may be tentatively assumed that dismemberment was effected near the scene of the attack,” Oscar noted.

The murderer likely killed her and then mutilated her body in the same location to avoid being caught with a corpse, he thought. As Oscar finished reassembling the mystery woman, an Oakland dentist confirmed her identity using a customized porcelain crown in her lower jawbone: Bessie Ferguson. She had recently been reported missing.

Oscar stood to the side while her mother wept. After her family left, Oscar stepped back and surveyed his ghastly jigsaw puzzle.

He had assembled a nearly complete skeleton of a woman who was once beautiful, provocative . . . and devious. Oscar had never met someone quite like Bessie Ferguson. But now he depended on her to reveal her killer.

*

From AMERICAN SHERLOCK: Murder, Forensics, and the Birth of American CSI by Kate Winkler Dawson, published by G. P. Putnam’s Sons, an imprint of the Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2020 by Kate Winkler Dawson.