In the fall of 1994, the United States was introduced to a new tool in the world of crime solving and prosecution — DNA evidence. The O.J. Simpson trial had captured the nation’s (if not much of the world’s) attention, and a large part of the trial’s outcome hung on DNA. At the time, the use of DNA evidence was still emerging, and the science wasn’t well understood — or trusted — by juries. (In September of 1994, the New York Times explored the issue. It’s a fascinating, contemporaneously-written glimpse into the history of law and science.) Even though the DNA evidence found at the crime scene in Simpson’s case was, by contemporary standards, almost certainly enough to secure a conviction, well, that’s not what happened.

But today, DNA evidence is almost always trusted and its findings dispositive. If a suspect’s DNA is found at a crime scene, he or she better have a good reason as to why. And on the flip side, the presence of someone else’s DNA (and the absence of the accused’s) can be used to demonstrate that the accused didn’t commit a crime. (Here’s a list of convictions overturned because of later-processed DNA evidence. There are a lot.)

So to summarize: if your DNA is at the crime scene, you’re in trouble; if someone else’s is there and yours is not, you’re in pretty good shape.


In January of 2009, a three-man jewel thief team pulled off a near-perfect crime. They broken into a Berlin department store named Kaufhaus des Westens and walked out with $6.8 million in goods. As TIME reported, the break-in was something straight out of a movie; “[the] masked, gloved thieves were caught on surveillance cameras sliding down ropes from the store’s skylights, outsmarting its sophisticated security system” — they couldn’t be identified on the security footage — and their latex gloves hid their fingerprints.

But one of the three robbers made a small and almost fatal mistake: he left one of those latex gloves behind. Authorities were able to pull a bead of sweat from it, and from that, get a read on the alleged thief’s DNA. Police ran the DNA through their database hoping to find a match. They didn’t find one.

They found two.

Specifically, they found Hassam and Abbas O. — their last names, pursuant to German law, were not released. But something more important was: the fact that they are identical twins. The brothers, age 27 at the time of the jewel heist, both had criminal records (a history of theft and fraud), and were therefore both in the database. Authorities knew that one one of them had left the sweaty glove behind, and, in hopes of determining which brother was the guilty party, arrested both.

The police didn’t get very far. Neither brother was willing to rat on the other — and their lawyers did not want them held in custody indefinitely. So the brothers went to court, demanding they either be formally accused of the crime or released. ABC News reported on the court’s finding: “From the evidence we have, we can deduce that at least one of the brothers took part in the crime, but it has not been possible to determine which one.”

Unable to avoid the genetically-built-in “it wasn’t me, it was him!” excuse, the court had no choice: the brothers were set free.

Bonus Fact: The verdict in the O.J. Simpson trial was so widely watched that it had a noticeable effect on phone use. As Wikipedia notes, long distance phone call volume dropped by 58% during the verdict’s announcement.

From the Archives: Yes, You Can Get a DNA Match for the Dog Poop You Just Stepped In: Because sometimes, you need to know which of your neighbors isn’t cleaning up after Fido.

Take the Quiz: A quiz on DNA. It’s hard.