Although there are standards for determining fingerprint patterns, the actual matching of them is entirely on the shoulders of the expert handling the case. As such, fingerprint identification is an extremely delicate art. And by "delicate," we mean "wildly subjective." Experiments have found that even highly respected experts can be biased, to the point where they can change their minds about the same exact set of fingerprints based on what they know about a case.

IgorKozeev/iStock/Getty Images
"He lost both hands while saving blind puppies from terrorists in Iraq."
"That's what they all say."

Still, old habits die hard. We've always been told that fingerprints are indisputable, and so that's what we believe. At least, right up until your brand-new fingerprint-scanning door slides open in the middle of the night and you find out that Strong Dong Johnson doesn't appreciate you taking credit for his work.

In the real world, tracking folks via their phones is less about triangulating signals before a killer hangs up and more about digging up cell phone records during the investigation phase. Cell phone towers can track the location of your phone to within a two-mile radius. That might not be accurate enough for them to pinpoint the Parkour Bandit and embark on an awesome rooftop chase, but it's more than enough to potentially ruin an alibi.

How It Can Go Horribly Wrong:

Cell phone tracking is widely used as evidence. In 2013 alone, U.S. courts saw a staggering 37,839 subpoenas, warrants, and court orders based on it. Which is kind of unfortunate, since cell phone tracking is inaccurate. So very, very inaccurate.

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"We got the perp. He's crossing into Egypt."
"Didn't this guy jack a car in Queens?"

Anyone who's dealt with a telecommunications company knows that cell phones are a huge clusterfuck at the best of times. Tracking via cell phone records is no exception. Your phone's not always going to choose the closest tower to have the best possible signal. The towers don't always have the same range, and there's plenty of overlap.

For an example of how this can go wrong, look at the case of Lisa Roberts, an ex-lover of a prostitute who was strangled in Portland, Oregon. Her cell phone data had "pinpointed" her in the area before the crime. She was forced to take a plea bargain of 15 years rather than a full 25 years in prison, and was only exonerated after serving 12 years.

KOIN-TV
"So, 'whoops' on that one ... How about we get you an iPhone and call it even?"

And yet the FBI continues to use cell phone tracking data as evidence. As of 2014, they had 32 full-time cell phone record investigators, and have trained 5,000 people to use the technology. They say two wrongs don't make a right, but surely 5,000 wrongs could make a right or two ...

Although hair analysis was a massively popular investigative tool in the 1980s and 1990s, there's a teensy, tiny little problem with it: "Matching" two hair samples is largely subjective. That's why Donald Gates isn't a unique case. A 2012 study looked into 268 cases in which the conviction hinged on hair samples, and found that a ridiculous 95 percent of the matches were deeply flawed.

"Well, we still caught, like, seven guilty guys, so I think that's a success."

According to the FBI, hair analysis isn't much better than judging somebody on their hairstyle. In 2015, they up and admitted that a "vast majority" of analysts in their elite forensic investigation squad have overstated their findings to help prosecutors get convictions. In hundreds of cases spanning 46 states. With dozens of the convicted ending up on death row.

Based on their hair.

Arson claims hundreds of lives and costs billions of dollars each year, so fire investigators come armed with complex methodologies, a vast knowledge of chemistry, and a burning desire to get to the truth (sorry, not sorry). Top facilities like the ATF fire research lab can practically reconstruct your last campfire with a poop sample from the bear that ate the ashes you left behind. Even at a lower level, there are strict guidelines for processing evidence.

How It Can Go Horribly Wrong:

Too bad a lot of their methodology is based on junk science and outright bullshit. What's worse, it's voluntary bullshit. Some arson investigators actively avoid keeping up to date with science. In 2004, an expert from the University of Cambridge estimated that fire investigators have falsely convicted thousands of people over the past 50 years. Take the case of David Lee Gavitt, a man who lost his wife and daughters in a fire in 1985. To make matters worse, Gavitt was promptly convicted for life, thanks to fire researchers going through the motions and falsely decreeing that the house had been doused with a gasoline-like substance. After 25 years of fighting the system and enjoying all the stigma of being a perceived child-killer, his conviction was finally overturned in 2012.

At this point, there should probably be an official "Our Bad" gavel.

There are arson investigators who base their methods on a predetermined rule-of-thumb collection: specific types of damage and char patterns mean an automatic arson call for them, and that's it. Unfortunately, research has proven that many of these presumed sure signs of arson can also happen during completely accidental fires.

Classic arson signs, like melted metals in doorway thresholds, can easily be caused by an ordinary fire that reaches flashover point and ignites the entire room. The list goes on and on. Our personal favorite is the crazing of windows, a phenomenon wherein glass suddenly develops hundreds of cracks. It's generally thought to be caused by rapid heating, thus indicating a fire that was lit with an accelerant. Turns out it can also easily be caused by rapid cooling -- such as, say, water from a fire hose striking a hot window. Whoever would have thought such a thing could occur at the scene of a fire?

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"I'm charging you all as accessories."

Expert witnesses can make sense of a difficult situation, and lend some professional authority to a statement that would otherwise amount to a long, wet fart noise in the ears of the jury. You can count on these folks to give an honest opinion on the matter at hand, based on nothing but cold, precise, well-researched facts and science.

Or can you?

No. Obviously, the answer is going to be no. You've read the rest of this article; you know that. Quit being coy.

How It Can Go Horribly Wrong:

One well-informed expert witness is fine and all, but such a marvel is practically nonexistent in the legal system. It's common for both defense and prosecution to call their own expert witnesses on a subject, and equally common for them to give contradictory opinions. In fact, courts do more than prepare for this schism -- they actually expect it. The U.S. legal system enables a judge to bring in another expert witness just to choose between the expert witnesses of the opposing sides.

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"Your honor, I'd like an expert witness to verify her expert credentials to verify the experts' expertise."

What's more, experts aren't even accountable for their antics. They are merely giving opinions. If they honestly believe they're right, even if they aren't, well, being wrong ain't illegal. If it was, anybody who doesn't like The Princess Bride would be in jail. Now, we're not saying that all experts are corrupt crooks selling their statements to the highest bidder. It's mostly down to unconscious bias. This means that each expert's opinion will be swayed to help the party they are working for, without intending any true malice.

Unlike those freaks who hate The Princess Bride. They're just plain evil.

Abraham is a Mexican lawyer. When he isn't doing law stuff, he writes comedy. You can say "Hi" to him on Twitter here, or visit his DeviantArt page here.

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