Rats in a Box

A special corollary of the Exasperated Perp. You've got three or more perps, all friends, relatives, or otherwise closely connected with each other, and none of them are talking. You know one or more of them committed the crime, but you've tried all the known (legal) tricks to get them to confess with no result. Solution: put the perps in one room, and let them stew in each other's presence until one or more of them snap. Sometimes it leads to a confession, usually it leads to the perps being worked up enough to finally respond to one last go-around in the interrogation room. Naturally, the detectives and security are always hanging just outside to intervene in case the shouting match that usually ensues in these kinds of situations leads to a physical confrontation between perps.

Trope named after an experiment that states if you leave a population of rats to stew and propagate inside a small box, eventually the rats will turn on each other for food and room.

This trope is, of course, the exact opposite of the classic "Prisoner's Dilemma" where you keep the prisoners apart and offer each one a reduced sentence if he rats out the other(s). Of course you make sure each one knows that his friends have received the same offer. It only takes one to break and the other(s) go down for life, but if I decide to talk first....

Comic Books

 * Played with in the Batman graphic novel The Long Halloween. A gang of Irish crooks are arrested for . They all confess, and their stories line up so perfectly that Batman and Gordon are convinced they're lying. They want the crooks to spill the name of their employer, hopefully Carmine "The Roman" Falcone, so Gordon locks them all in the one big cell hoping that they'll get chatty. The catch is,

Literature

 * Done in the Lord Peter Wimsey mystery The Nine Tailors. Neither Wimsey nor the police can figure out which of two brothers murdered the victim, so they put the brothers alone in a room and secretly listen to what they say to each other.
 * Sped up brilliantly in Night Watch. Vimes finds he has three assassins in custody, two of whom are thoroughly professional, but the third is a showoffy twerp; Vimes classifies him as "the sort that gets a kick out of showing his dagger to women in bars". So, enjoying a ham and hoosegow sandwich, he drags the two others in back, but leaves the door open so Showoff Dan (who Vimes has dubbed "Ferret" for his weaselly demeanor) can hear all the screaming. Before he gets a chance to even grab the keys so Ferret can have his turn, the guy spills-and Vimes reveals that the screaming was just him and the boys goofing around. Ferret starts doing some mental arithmetic, then demands protective custody in return for ponying up everything else he knows.

Live Action TV

 * Done in Burn Notice, when the second rat is the main character, trying to get some information out of the baddie by pretending to be a previously-unknown colleague.
 * British intelligence once actually did that by putting spies disguised as Luftwaffe pilots in the same room with prisoners. It worked quite well.
 * The Commish. In this case the guilty party was the one who fell asleep in the prison cell (apparently Truth in Television as it was mentioned in the non-fiction book Homicide: A Year On The Killing Streets. Based on the idea that the others don't know why they've been arrested, but the guilty party is resigned to the fact that he's been caught).
 * In Season 2 of 24, CTU agents put Bob Warner and Reza Nayieer in a room together in order to determine who transferred the funds to Abu Fayed. Reza cracks and offers to show the CTU agents how the funds were transfered,.

Truth in Television

 * Another variation combines Rats in A Box and the Prisoner's Dilemma: one perp is taken away from the others, then immediately reinserted into the group solely to instill suspicion. For instance, the cops sits one of the perps in the interrogation room, then stand in total silence for some amount of time while the perp looks on in puzzlement. Then the cops return the perp to his accomplices, who ask what the cops wanted with him. The perp honestly replies "nothing", but now the suspicion that the cops offered him a deal is planted in everyone else's mind, and group solidarity quickly collapses. Tritter uses a variation of this in House.
 * A variation has the above, then the guards acting suspiciously nice to the person they took away. Your comrades thinking you already took a deal is quite a bit of pressure to actually take it.