Let’s say someone who was convicted due to an expert’s diagnosis of “shaken baby syndrome” wants to file a post-conviction petition based onthe growing consensus that the theory is flawed. At what point does that year-long window to file the petition begin to start? Is it after the first critical study? The second? Is it once the scientific community has reached a consensus? What defines a “consensus?” How do you define the field of scientists among which a consensus must arise?
From the prospective of the wrongly convicted, you can see the trap, here. File too soon, and the court may conclude that you haven’t presented enough evidence that the forensic theory upon which you were convicted has been discredited. If you then try to file more petitions as more evidence comes out to bolster your argument, you risk the court concluding that this is an issue you’ve already raised, you lost, and you’re therefore barred from raising it again.
Here’s a real-world example: Mississippi courts, prosecutors, and attorneys general continued to uphold and defend the credibility of the now notorious bite mark analyst Michael West well into the mid-2000s. This, despite the fact that West had been repeatedly exposed as a fraud going back to the mid-1990s. He had even been ostracized within the already controversial and scientifically suspect community of bite mark analysts. Mississippi Attorney General Jim Hood finally conceded only a couple of years ago that West wasn’t a credible witness. But while Hood’s office had by then stopped defending West’s credibility in court, the office continued to defend convictions won on West’s testimony. Hood’s staff did so by arguing that defendants who had already challenged West’s credibility at trial, on appeal, or in previous post-conviction petitions, and lost, were procedurally barred from raising that claim again. Thus, defendants are stuck: File too soon and you’ll lose on the merits and risk being barred from raising the claim when more evidence comes out. But if you wait for more evidence, you risk running afoul of the deadlines on newly discovered evidence.
So let’s get back to James Koon. Forensic pathology (the field practiced by medical examiners) is a particularly tricky area of forensics because it’s both objective and subjective. “There are four bullet holes in the victim’s heart” is an objective statement. You’ll rarely find two medical examiners arguing such a point. “The bullet’s trajectory suggests that the killer shot the victim while standing” is far more subjective. It may be true. But it’s confounded by variables, such as the body positions of the shooter and victim, the elevation of both, the angle at which the killer was holding the gun, and so on. How much stock the jury puts in a medical examiner’s testimony on such questions relies heavily on how credible the jury finds the medical examiner. This is particularly true if the defense has its own medical examiner with contradictory opinions. (Perversely, this is a system that rewards people who sound convincing to juries. A medical examiner who speaks in certainties will sometimes sound more persuasive to a jury than one who hedges his opinions and refuses to speak in absolutes, even though the latter is usually the more scientifically sound approach.)
In some cases, forensic experts have been clearly exposed as frauds, such as cases in which a crime lab technician was shown to have faked test results. Here, there’s a clear time for the clock to start running on that window to file a petition. In other cases, such as Hayne, the information has come out in a stream, so it’s far less clear.