Six perfect strangers assemble to pull off the perfect crime, but when their simple robbery explodes into bloody ambush, the ruthless killers must work out which one amongst them is a police informer.

Ambushed after an attempt to commit the perfect crime, robbers try to figure out which of them acted as a police informer.

Hey there! I think I get your idea, but maybe it's a little fragmented.
1. The six strangers are ruthless killers.
2. Somehow they come together to pull of a perfect crime.
3. While they're doing a simple robbery they realize they're actually in an ambush.
4. One of them is a police informer, they need to find out who.

Okay, so. Maybe you should tell in the beginning that the strangers are killers (otherwise we might get the idea that they are just normal joes). Also, they are doing the perfect crime which turns out it's just a simple robbery?
I see an interesting idea in there, just wished the logline was more organized! Good work!