If you were charged with a crime in the U.S. and put on trial, would you assume that the forensic evidence introduced in court against you would at least be based on some kind of sound, factual, scientific research? Think again.
Frontline recently ran a documentary on the "science" of fingerprinting, bite mark analysis, and other forensic "sciences" and demonstrated rather convincingly that many courts will allow testimony by self-styled experts that has no basis in any substantive research whatsoever.
The most dramatic examples were related to two men who had been in prison for ten years or more for assaulting and murdering three-year-old girls. In both cases, the men were the former boyfriends of the girls' mother. In both cases, an orthodontist who claimed to be versed in the science of bite mark analysis testified that scratches on the little girls' bodies were actually bite marks that could only have come from the suspects, to the exclusion of everyone else. In each case, this testimony was the bulwark of the prosecution's argument. In each case, the judge allowed the testimony. In each case, the man was convicted. In each case, DNA analysis-- which is founded in real science-- eventually exonerated the men, and the real killer confessed to the crimes.
Do I have to be polite when expressing myself about how I feel about these judges for allowing this testimony into their courts? This is not a matter upon which reasonable, educated people might respectfully beg to differ. These are witch trials that have no place in a civil society.
How far does it go? At the Casey Anthony trial a self-styled expert in smells testified that a container of smell-- I'm not making this up-- from the trunk of Casey Anthony's car contained the smell of a dead body. Casey Anthony was found not guilty largely because she was able to raise $200,000 for decent lawyers by selling pictures of her with Caylee to People Magazine. Those lawyers successfully challenged a host of junk science evidence.
Now, there are rules about "expert" testimony. Prosecutors interviewed by Frontline didn't seem aware of them. One of them declared that it was up to the jury to determine whether the smell evidence was truthful, relevant, or accurate. It is not. The Supreme Court has ruled that the judge is the "gatekeeper" for expert testimony and determines whether any specific evidence should be presented or not. Furthermore, evidence will be deemed qualified if it has been gathered according to a scientific methodology which makes use of valid scientific procedures. One key element is falsifiability.
That said, some judges will permit both sides to present evidence on the scientific validity of certain procedures and expect the jury to sort it out. This gives an enormous advantage to the heavily resourced prosecution in most cases.