There are a few hard sciences like toxicology and DNA. But even DNA has subjective elements, we're learning, when lab analysts interpret DNA mixtures.
I've found myself explaining to several different folk recently why so many forensic disciplines all of a sudden find themselves questioned, so thought I'd share that spiel with readers. The debate really took hold after 2009, when the National Academy of Sciences issued a major report titled "Strengthening Forensic Science: A Path Forward." That expert review called into question numerous forensic disciplines in a fundamental way, particularly undermining the scientific credentials of comparative forensic disciplines from fingerprints to tool marks.
Of the comparative forensics - where somebody sits with a microscope and compares two bullet casings, hair follicles, bite marks, fingerprints, etc. - these are mostly not fields developed through application of the scientific method. Indeed, many of them have little formal scientific underpinning at all. They're just things cops began doing at some point in history (principally post-Arthur Conan Doyle) to accuse people of crimes.
No one develops expertise comparing hair follicles under a microscope, for example, unless they're paid by the state to try to match evidence to suspects in criminal cases (though they're not supposed to say "match"). It's not like there's an independent source of expertise defense attorneys can turn to in such instances - nobody does that work except other crime labs, whose analysts were probably all trained at the same FBI schools as the state's expert.
That's not to say that, being unscientific, these comparative disciplines are necessarily invalid. They're just more craft than science. Experienced, expert examiners can tell a lot about the evidence they look at. But it's at root a subjective, not a scientific process, regardless of the trappings. The NAS report laid that history bare.
Then there are other disciplines - like arson investigation and diagnoses of "shaken-baby syndrome" - where prior conclusions have been abandoned in light of more recent scientific developments. Texas' new and improved junk science writ makes this state an important site for litigating these issues over the next few years, so expect to hear about these topics more in the future. We're at the front end of a period when traditional forensics are being reevaluated, in many cases for the first time.
Here is Grits' list of top five junky forensic "sciences," all of which are either currently under scrutiny or predictably will be in the near future, with a few dishonorable mentions tacked on since five is awfully short for this list. They're in no particular order and represent my own opinion and no one else's. I could probably even be convinced to drop one or two off the list and add others (make your case in the comments). I offer the following up only as an off-the-cuff thought experiment, not a definitive account. With that said:
Bite marks have been known to be on the junky end for a while, so they're only rarely used. However, prosecutors bring them in when they need that little extra push to get over the hump in a tough-to-prove case. Texas' review of bite marks cases (aka, "forensic odontology") kicks off in Dallas when a committee of the Forensic Science Commission meets in Dallas today (Wednesday) to consider the issue.
This field arguably is more valid than bite marks - a compliment akin to "prettier in a dress than Dennis Rodman" - but was made nearly anachronistic by mitochondrial DNA testing, which is far more precise. Now, modern science and statistics have demonstrated that many analysts, particularly in older cases, routinely overstated the extent to which they could match suspects to evidence in court (for instance, they can't say "match" or even estimate statistical probabilities, since that overstates what could really be known about individualization of evidence from even the most expert review). The Texas Forensic Science Commission has begun reviewing old cases, mirroring a similar effort reviewing hair microscopy at the FBI. But the going is slow and made more difficult by problems getting transcripts from the appellate courts; there's a significant number of these cases out there.
Shaken Baby Syndrome
The New York Times called it "A Diagnosis that Divides the Medical World." Biomechanical research has debunked many of the early claims, but proponents remain dug in. Emotions run so high whenever someone thinks a caregiver murdered a child that science can become lost in the shouting. The Washington Post published a major piece this spring examining the state of the debate. These cases aren't legion but neither are their numbers insignificant. And the defendants are disproportionately women.
Another science-free field whose validity has been long debated, you'd think this one may eventually go extinct altogether. Analysts' associations are 95% accurate when they have four-page documents to compare, but who writes that much anymore? OTOH, when it comes to identifying forgers from signatures on checks: ''Even in laboratory settings, there is no evidence they can do it."
Abel Assessment/Penile Plethysmograph
These gems are used particularly on the parole side: They show alleged sex offenders dirty pictures and measure their responses, in the case of a plethysmograph by attaching measuring devices to the penis. Various studies have estimated the error rate on the Abel Assessment at 35-48%. One study found "a 42 percent false-positive rate when non-molesters were tested."
- Dog-Scent Lineups (defunct in Texas, last known uses in Florida, communist Cuba). Former Ft. Bend Sheriff's Deputy Keith Pikett's dogs supposedly performed scent lineups in many hundreds of criminal cases, but nobody's ever tracked them all down.
- Comparative bullet-lead analysis (defunct). As it turned out, an Aggie helped kill it.
- Arson (older cases - Grits readers will recall the problems with arson science raised in the Todd Willingham case, the FSC, and the State Fire Marshall's arson review). Modern, 21st century arson investigation is much more science-based, derived after burning down hundreds of test buildings and gathering evidence. Under modern standards, arson investigators are also more likely to label a fire "inconclusive" than "arson"; many of the old indicators have been debunked but not always replaced.
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