Tag Archives: forensics

Truth nuggets

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If you watch crime shows, you’ve seen it a zillion times. A crime happens. The attractively dressed detectives gather evidence (or at least stand around looking good while someone else does). The evidence goes to the lab. Minutes later, the lab has an answer. And zap! the bad guy’s in custody, soon to be followed by a conviction. Roll credits.

Makes for a good story, but that’s not how things really work. Several truth nuggets about this scenario:

  1. Over 80% of arrests are made by uniformed officers, not detectives.
  2. Real detectives are generally not as pretty as the ones on TV, and they definitely don’t dress as well.
  3. A large percentage of crimes have little or no physical evidence—so there’s nothing to send to the lab. Or if there is any physical evidence, it’s of little value. When I was in college, I got robbed at gunpoint in the deli where I worked. The cops dusted the counter for prints, but dozens of people had touched that counter since I last wiped it. The chances of getting quality prints of the perp were about zero.
  4. Labs are backlogged. Sometimes for years. Even in an important, high-profile case, it will take many months before lab results are in.
  5. Scientific testing is not infallible. Lots of things can go wrong. Evidence can be mishandled. The lab tech may be unqualified or inept; there have even been cases where they deliberately falsified evidence. The science itself may not be as reliable or as valid as we assume. Even such a seemingly simple scientific technique as fingerprint analysis has been questioned.

I think all these truth nuggets can be exploited to craft a story that’s fresh and cliche-free. They create a host of plot possibilities. So use them!

Plot bunny: olde tyme forensics

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Usually I focus these posts on the criminal justice system in the modern US. But today I’m veering from that a bit to give you a plot bunny. This one might come in handy if you’re writing a historical or spec fic.

We generally think of forensics—the use of science to help solve crimes—as a modern phenomenon. Certainly, in recent years we’ve made much wider and more frequent use of forensics, and science has made huge advancements. But even hundreds of years ago, science was occasionally used in criminal cases.

As far as I can tell, the earliest documented example of this was a Chinese judge named Song Ci, who was born in the late 12th century. He wrote a textbook called Washing Away of Wrongs. Among other things, his book described an early use of forensic entomology, or the use of insects as crime evidence.

Your book’s setting might not allow for state-of-the-art DNA analysis or spectroscopic analysis of paint samples. But even if your book is set in a pre-industrialized locale, you could take inspiration from Song Ci and make use of some scientific detection methods.

The truth about science and crime

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Every crime show ever.

Setting—messy crime scene

Attractive Detective 1: Wow, look at all this blood and semen so helpfully spread all over the crime scene!

Attractive Detective 2: I will collect it and rush it to the crime lab, pronto!

5 minutes later,  setting—gleaming hi-tech crime lab

AD 2, handing evidence to Attractive Lab Tech: This case is super important. We need results pronto!

ALT: Right on it, Detective.

5 minutes later

ALT: Here you go, Detective. Yep, all the DNA definitely belongs to Slimy Suspect. I’m 100% sure.

AD2: Great, thank you!

5 minutes later, setting—courtroom

Stern Judge: I sentence you, Slimy Suspect, to life in prison!

How many times have you watched TV shows with essentially this scenario? There are many inaccuracies here, but today I’m going to focus on one, involving that crime lab.

On TV, the lab gets the evidence and analyzes it, and the suspect promptly finds himself whisked off to jail. In reality, though, evidence analysis takes time. Most of this is due to high demand and limited capacity. It’s estimated that the current backlog may include well over 350,000 cases. And it’s not just DNA from crime scenes, but also drug testing and evidence from rape kits. Depending on the jurisdiction and the case, it may take over a year to get results back from the lab.

Time isn’t the only problem. Labs range in quality and not all are accredited. Their employees also vary in accuracy. There have been numerous reported cases of lab employees making errors in their work, either by accident or on purpose.

And even the best employees of the best labs can’t always get wonderful results. Forensic evidence can degrade or be contaminated. To give a personal example of this, when I was in college and working at a deli, I was robbed at gunpoint. When the police came, they dusted the counter for prints, but we all knew that was a pretty useless activity. Over the course of the day, dozens of people had touched that counter, so distinguishing the robber’s prints from everyone else’s would have been impossible. (They never caught anyone for the crime.)

And even when the evidence is in great shape, an analysis can never deliver absolute certainty. The best it can do is offer a probability of a match. And if the (innocent) suspect has an evil identical twin, he may be out of luck.

Finally it should be noted that DNA and similar evidence isn’t present at most crime scenes. If someone robs a bank, she’s probably not going to leave behind blood or anything else that is an obvious source of DNA evidence.

So those pretty detectives and lab techs might make for fun TV viewing, but they have little to do with law enforcement reality.