Since this seems a 'bash on clowns' day, let's move to forensics

But criminal forensics has a deeper problem of basic validity. Bite marks, blood-splatter patterns, ballistics, and hair, fiber and handwriting analysis sound compelling in the courtroom, but much of the “science” behind forensic science rests on surprisingly shaky foundations. Many well-established forms of evidence are the product of highly subjective analysis by people with minimal credentials—according to the American Society of Crime Laboratory Directors, no advanced degree is required for a career in forensics. And even the most experienced and respected professionals can come to inaccurate conclusions, because the body of research behind the majority of the forensic sciences is incomplete, and the established methodologies are often inexact. “There is no scientific foundation for it,” says Arizona State University law professor Michael Saks. “As you begin to unpack it you find it’s a lot of loosey-goosey stuff.”

Not surprisingly, a movement to reform the way forensics is done in the U.S. is gaining momentum. The call for change has been fueled by some embarrassing failures, even at the highest levels of law enforcement. After the 2004 train bombings in Madrid, Spain, the FBI arrested Oregon lawyer Brandon Mayfield and kept him in jail for two weeks. His incarceration was based on a purported fingerprint match to a print found on a bag of detonators discovered near the scene of the crime. As a later investigation by the Justice Department revealed, the FBI’s fingerprint-analysis software never actually matched Mayfield to the suspect fingerprint, but produced him as an “unusually close nonmatch.” Lacking any statistical context for how rare such similarities are, investigators quickly convinced themselves that Mayfield was the prime suspect.

Couple of years ago there was a case that trashed a method the FBI lab had used for many years. They had contended that if you analyzed the content of a bullet you could state with certainty that, for instance, the bullet found at a crime scene came from the box of cartridges found at a suspect's home; turned out not to be true. It seems that a batch of melted lead doesn't form a perfectly homogeneous mass; some of the alloying elements can concentrate in 'batches' in the mass, causing bullets from the same box to have slightly different analysis. A defense attorney finally had a lab actually test what the FBI was claiming, and oops!

And, on the subject of those 'ballistic fingerprints',
Ballistics has similar flaws. A subsection of tool-mark analysis, ballistics matching is predicated on the theory that when a bullet is fired, unique marks are left on the slug by the barrel of the gun. Consequently, two bullets fired from the same gun should bear the identical marks. Yet there are no accepted standards for what constitutes a match between bullets. Juries are left to trust expert witnesses. “‘I know it when I see it’ is often an acceptable response,” says Adina Schwartz, a law professor and ballistics expert with the John Jay College of Criminal Justice.
Isn't THAT just a wonderful thing to trust you life and liberty to? And screw with the 2nd Amendment for?

And here's the end of the article:
It will take years to fully reconcile the rigors of the scientific method with the needs and processes of the judicial system. But in the meantime, questionable forensic science will continue to tip the scales of justice. And when bad decisions are made in the courtroom, an innocent person’s entire life can be swept right out from under him. It happened to Steven Barnes 20 years ago. Then 23 years old, he was brought to trial for the rape and murder of a 16-year-old girl. He had never been arrested before and was confident he’d be cleared. Yet he watched as forensics expert Elaine Pagliaro testified that two hairs found in Barnes’s pickup were microscopically similar to the victim’s. Pagliaro also noted that soil samples taken from the truck were consistent with dirt from the crime scene and even that a distinctive pattern from the victim’s jeans was similar to an imprint left on the truck.

Due largely to her testimony, Barnes was sentenced to 25 years to life in prison. Last year, he was cleared by DNA and released. He’d never been on the Internet or used a cellular phone, and his girlfriend, who initially stuck by him after he went to prison, had long ago married another man. Barnes told Popular Mechanics that he works hard not to be overwhelmed by bitterness, even toward the jurors. “They must have thought, ‘[Pagliaro] knows what she is talking about.’”

Pagliaro, a veteran analyst with the Connecticut State Police, has recently co-authored a book called The Real World of a Forensic Scientist. “I think this scrutiny is actually good,” she says. “It’s important for the public to have a realistic expectation of what the science can do.” As for the Barnes case, there is no suggestion of impropriety regarding her testimony, but none of the evidence she presented was based on statistically validated science. “You feel awful someone spent all that time in jail,” she says. “All you can do is look back and say, ‘Was that the best we could do?’”

Well, Pagliaro, I'm sure it does people you wrongly put in jail a friggin' WORLD of good to know you wonder 'if that was the best you could do?' Especially any who might still be behind bars because of you.

And there are prosecutors who will fight tooth and nail against having DNA evidence tested in past cases; they tend to argue it's 'unnecessary' and 'too expensive'. Sometimes, probably because they're scared that it might prove they put the wrong man in prison and don't have the integrity to face it if that's the case.

Oh, more on 'ballistic fingerprinting' from the second article:
As with fingerprints, not enough research has been done to quantify the probability of error in ballistics matching. So it’s impossible to say with certainty that the marks made on bullets as they are fired are truly unique to an individual gun. Currently, ballistics examiners are aided by computer databases such as the ATF’s National Integrated Ballistic Information Network, but lab techs always rely on their own visual inspection to make the final call. The Association of Firearm and Tool Mark Examiners only requires an examiner to find “sufficient agreement” between bullets in order to conclude that they came from the same gun. Those judgment calls can cause false results. Last September the Detroit Police Department’s crime lab was shut down after an audit by the state of Michigan found a 10 percent error rate in ballistics identification.