Interrogations Can Get Innocent People to Confess
Remember what it was like to accuse a sibling of stealing a favorite possession? No matter how hard they protested or how strongly they insisted that maybe you should take a peek at that shithole you were calling a bedroom, it didn't matter. Your Jem and the Holograms cassette was stolen, and you knew who took it.
Suspect interrogation is kind of like that. If the interrogator is convinced the suspect is guilty before the interrogation starts, it's hard to change his mind. He or she will assume everything from cries of innocence to constant crotch-scratching is proof of guilt, which leads to a more aggressive line of questioning. But who cares? If the bad guy confesses, the good guys win -- it's the one time you know for sure you got the right guy. That's why just about any confession makes a jury more likely to convict, even if the jury is told that the confession was coerced. After all, no matter what, an innocent person isn't going to confess to something he didn't do.
"That's right, little Jen. Just confess to selling all that coke and we'll buy you some cotton candy."
So What's the Problem?
Wrong. It happens all the time. And we mean all the time. In one famous 1989 case of a rape of a jogger in Central Park, five men went to jail after the cops got them to confess to the assault. Then they were released, after it turned out they didn't do it (another guy already serving time for a different assault finally came forward).
"Only the guilty have anything to fear. And the innocent, if we're having a slow day."
It turns out it's actually not all that hard to get a confession out of an innocent person. The same high-pressure psychological techniques meant to wear down a guilty suspect will make a lot of innocent people confess to something they didn't do. Since innocent people are more likely than criminals to waive their right to remain silent, they're put in a high-stress situation where they're not even clear about what they're being charged with. They also may feel guilt for some unrelated reason (they saw the crime and failed to report or stop it, for example). So, they say whatever they need to say to make the interrogation end.