In 1994 Eddie Lee Howard was convicted of raping and murdering 84-year-old Georgia Kemp. Kemp was found dead in her Columbus, Mississippi, home by firefighters after a neighbor noticed smoke coming from the house. Investigators determined the fire was set intentionally.

Kemp's body was taken to controversial Mississippi medical examiner Steven Hayne, who would later lose his lucrative niche as the state's go-to guy for autopsies after years of criticism for sloppy work that rarely failed to confirm prosecutors' suspicions. Hayne concluded that Kemp died of knife wounds and said he found signs of rape, although the rape kit taken from Kemp turned up no biological evidence that the technology available at the time could test for DNA.

Three days after Kemp was buried, District Attorney Forrest Allgood, the chief prosecutor for the four counties of Mississippi's 16th District, zeroed in on Howard, who at the time was unemployed and living with a relative down the street from Kemp's house, as the culprit. Once Howard was identified as a suspect, Hayne suddenly recalled seeing marks on Kemp's body that could have been made by human teeth (Hayne's original autopsy report makes no mention of the bite marks). So Kemp's body was exhumed and given to Hattiesburg, Mississippi, dentist Michael West, a self-proclaimed expert in bite mark analysis and frequent beneficiary of Hayne's referrals. West confirmed that the marks were indeed bite impressions and that some of them could only have been made by Howard's upper teeth—a puzzling claim, since Howard's upper teeth were a mass-manufactured denture. Howard was convicted and sentenced to death in 1994. The Mississippi Supreme Court later gave Howard a new trial, ruling he was unfit to represent himself at trial. He was again convicted and again sentenced to death in 2000.

West's bite mark testimony is the only physical evidence linking Howard to the crime scene. (The other evidence against Howard includes incriminating statements he allegedly made to a police officer that were not recorded or written down and testimony from an ex-girlfriend that Howard smelled of smoke the day after Kemp's murder.) At the time of Howard's conviction, West was a star forensic witness, claiming to have perfected a method of bite mark analysis no other forensic specialist could duplicate. But since Howard's conviction, West has become the poster boy for forensic fakery.

West, who once claimed he could trace the tooth marks in a half-eaten bologna sandwich at a crime scene to a defendant while excluding everyone else on the planet, has had to resign from two professional forensics organizations due to his habit of giving testimony unsupported by science. In 2001 (as I reported last year) a defense lawyer caught West in a sting aimed at revealing him as a charlatan: West matched the dental mold of a private investigator to unrelated photos of bite marks from a crime committed eight years earlier. West even sent back a video in which he methodically went through his technique. Despite all this, the Mississippi Supreme Court upheld Howard's conviction and death sentence in 2006. With respect to West, the majority concluded, "Just because Dr. West has been wrong a lot, does not mean, without something more, that he was wrong here."

Since then a wave of new revelations (described in more detail below) has confirmed that Steven Hayne and Michael West are not credible expert witnesses. Last month Howard and his attorneys at the Mississippi Innocence Project cited some of that evidence in asking the Mississippi Supreme Court for a new trial. In response, Mississippi Attorney General Jim Hood does not argue that Michael West is a credible expert or that his testimony in Howard's case had any scientific foundation. Instead Hood argues that because the Mississippi Supreme Court already has upheld West's testimony in the face of criticism, Howard is procedurally barred from again citing West's quackery in a bid for a new trial.

The argument may arguably be legally correct, but Hood is not obligated to make it. Hood, whose duty is not just to win cases but to pursue justice, should have the decency to review every case in which West has ever testified. Instead, in the face of growing evidence that the criminal justice system he presides over has been corrupted by unreliable expert witnesses, Hood is essentially arguing that Eddie Lee Howard should be sent to the death chamber on a technicality.

The new evidence against Hayne and West is compelling. In 2008 Kennedy Brewer and Levon Brooks were released from the Mississippi State Penitentiary in Parchman after serving nearly 30 years between them. Both were convicted of raping and murdering young girls near Columbus, Mississippi. In both cases, District Attorney Forrest Allgood, the same man who prosecuted Howard, took the girls' bodies to Hayne. In both cases, Hayne found marks on the bodies he declared to be human bite marks, a claim other forensic experts have since disputed. In both cases, Hayne called in West, who matched the bite marks to a dental mold taken from the man Allgood thought committed the crime. Brewer and Brooks were exonerated and released when DNA evidence showed a different man, Albert Johnson, committed both crimes.

Last year I reported on the Louisiana case of Jimmie Duncan, convicted in 1998 of murdering 2-year-old Haley Oliveaux. Once again Hayne and West found bite marks on the victim's body that other doctors didn't see and supposedly traced them to the prosecutor's chief suspect. In that case, there is a video of West repeatedly jamming a dental mold of Duncan's teeth into the little girl's corpse, an act that forensic specialists told me is at best medical malpractice and probably constitutes criminal evidence tampering. Duncan is still on death row.

West used his bite mark magic to condemn Brooks in 1990, Brewer in 1992, and Duncan in 1993. He matched bite marks to Howard in 1992.

There is no question that West's testimony was critical to Howard's conviction. Allgood's laudatory description of West during the second trial was so hyperbolic that it verged on parody, implying that the jurors' grandchildren would read about the daring dentist in textbooks. "Whether we like to think so or not," Allgood said, "the progress of mankind has been carried forward on the backs of people like Michael West. The church threatened to burn Copernicus because he dared to say that the planets didn't revolve around the earth. So it was with Michael West." This view of West is so grotesquely at odds with his real-life quackery that Allgood's confusion of Copernicus with Galileo seems trivial by comparison.

Howard's brief also cites a 2008 National Academy of Sciences (NAS) report questioning the quality of forensic science used in America's courtrooms. The report is especially critical of the bite mark analysis performed by specialists like West. The authors found no scientific support for the notion that someone can match bite marks left on skin to one person, certainly not to the exclusion of everyone else on Earth, a claim West frequently made in court. The NAS report, which was commissioned by Congress and reviewed by a panel of scientists, suggests that courts never should have accepted bite mark analysis as evidence and calls into question convictions based on such testimony.

Hood dismisses the NAS report, arguing that "the arguments against bite-mark evidence testimony found in the report are the very ones argued by the petitioner and those that have been argued in the courts for many years." In other words, the conclusions from a panel of respected scientists who confirm the arguments that West's critics have been making for years should be viewed as irrelevant, precisely because West's critics have been making those arguments for years, and Mississippi's courts have rejected them. That the critics were right and the courts were wrong does not matter. Sadly, Hood's argument has legal merit.

It gets worse. The state's brief goes on to claim that the NAS report "itself acknowledged that bite-mark testimony is reliable." To support that assertion, the brief cites this quote from the report: "Despite the inherent weaknesses involved in bite mark comparison, it is reasonable to assume that the process can sometimes reliably exclude suspects." Yes, one can envision a scenario where, for example, a very clear bite mark showing a full set of front teeth could exclude a suspect who has no front teeth. But in Howard's case, West claimed he could trace bite marks left in the victim's skin days earlier to Howard and only Howard. The NAS report clearly states that such a feat is impossible.

One other distinction is worth noting. The NAS report was critical of all bite mark evidence. But even among bite mark analysts, West is an outcast. That is, he is a disgrace even by the standards of a discredited field. Yet Hood is ready to execute a man based largely on West's testimony.

Although Howard's brief doesn't mention it, the credibility of Hayne, West's collaborator, also has been called into question since Howard's last appeal. Hayne was the subject of a 2007 exposé that I wrote for Reason and the target of a 2008 complaint in which the Mississippi Innocence Project asked the state medical board to revoke Hayne's license. In 2008 Mississippi Public Safety Commissioner Steve Simpson effectively barred Hayne from doing any more autopsies in the state. Last year Hayne resigned from the National Association of Medical Examiners in the face of a pending ethics inquiry. But as I reported earlier this year, Hood, who also used Hayne when he was a D.A., has resisted any systematic review of old cases that may have been tainted by Hayne's testimony and even led a fight to let Hayne do autopsies again.

In the last few years, Hood has come under fire from The Wall Street Journal and other critics for his cozy relationship with the plaintiff's bar, particularly with convicted felon Dickie Scruggs. Hood's response to the criticism has been that he is merely a fighter for the little guy. That boast must ring hollow for the little guys wrongly sucked into the state's broken criminal justice system.

Radley Balko is a senior editor at Reason magazine.