Plea bargaining is a bedrock of our criminal justice system. Governments simply don't have the money to take every criminal defendant to trial. They rely on the fact that a large proportion of defendants will opt for a plea deal if it means less prison time.
Scientifically, it's a pipe dream. It would be convenient if we could train law enforcement officers on how to tell if people are lying, but so far there is no way to do so. That doesn't stop people from trying, though.
Recently, a New Mexico newspaper and the Associated Press covered what sounded like a light-hearted story. Apparently, someone attempted an armed robbery a Pizza Hut store in Las Cruces.
It may be true that no two sets of fingerprints are alike, although there is no actual study showing that. Even if it is true, however, the process of matching fingerprints found at crime scenes to prints from other sources is messy. Most often, crime scene prints are partial or smudged, and there are plenty of prints that are thought common enough to match these.
Each year in the United States, about a million people are pulled over on suspicion of drunk driving. In virtually all of those cases, the driver is asked to blow into a breathalyzer-style machine that estimates their blood-alcohol content. If it's above a certain level, typically 0.08%, the driver is arrested and brought to the precinct for additional testing.
In 2009, the National Academy of Sciences (NAS) issued a blockbuster report challenging the scientific underpinnings of many fields of forensic evidence. The report found that such evidence is rarely supported by rigorous study. Moreover, the analyses are often performed unscientifically, and analysts often overstate the scientific rigor of their evidence during testimony.
In 2009, the National Academy of Sciences issued a blockbuster report on the state of the science in forensic investigation. That report concluded that, "with the exception of nuclear DNA analysis ... no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source."
A jailhouse informant is rarely someone who just wants to help. Jails and prisons have a strong anti-snitching culture, so passing along information to prosecutors is a choice that could get you in serious trouble. People don't inform on other prisoners to be solid citizens; they do it to get a break on their sentences.
Polygraph tests, often called "lie-detector tests," are not admissible as evidence in the courts. This is because they have never been shown to produce reliable proof of whether the subject is lying.
We've discussed on this blog how genealogy databases like GEDmatch warehouse the DNA results of huge numbers of people who have taken part in genetic testing for genealogy purposes.