The cops have found the perpetrator of the crime they're investigating. The thing is, he's got a gun—perhaps one whose magazine is dripping with ammo. Or he's got a bomb. Or he's poured petrol (gasoline if you're American) all over the place and has a lighter.
The sequence goes like this:
- Perp yells at lead detective something along the lines of, "I'm gonna take you all down!"
- Lead detective says "Don't do anything stupid," and then "We can talk about this".
- A discussion follows, during which the detective feigns sympathy for the perp and the perp confesses to the crime.
- Eventually, the perp drops the weapon and then comes out with his hands up.
- The detective drops the sympathy, slams the perp against the wall, and handcuffs him.
A Dirty Cop
will probably do worse than slamming perps against the wall.
- Law & Order and its various spin-offs use this trope liberally.
- CSI: Crime Scene Investigation
- The American version of Life On Mars had Sam Tyler do this at one point.
- A letter-perfect example happens to the hero of Conspiracy Theory.
- Criminal Minds does this quite often, but they usually end a lot less happily, as the unsub usually ends up blowing his own brains out, or ignoring the cop and goes trigger happy, leading to a similar demise.
- One particularly depressing episode had a war veteran who believed he was still in a war hiding from the enemy. The cops surrounded the place with snipers and told him to surrender, and the veteran saw a small child, and ran toward him telling him to get away or he'd be killed. The cops thought he was going to kill the child, so they killed him before he could get to him.
- Bookhunter uses this in its Batman Cold Open. When the library police apprehend a book thief, they find him dousing the books in gasoline, holding a lit match, and threatening to burn everything down if the cops don't back off. Agent Bay solves this the Cowboy Cop way: he uses the recoil from a shotgun to propel himself across the room, then shoots the perp at just the right angle that his blood spatter extinguishes the match.