This is apparently an interview question from Black Rock.
-------------------------------------$
Murders in a field.

You are guarding 100 murders in a field and you have a gun with a single bullet. If only one of the murderers has a non-zero probability of surviving, he will attempt to escape. If a murderer is certain of death, he will not attempt escape.

How do you stop them from escaping.

//
This question is so interesting so I thought I would give it a go of how I would answer.

I would announce to the prisoners.

That I have a kill switch, if I die the surrounding area is set to explode killing everyone. I walk around with the gun pointed to my head and a rubber band on the trigger finger, meaning if I get incapacitated the gun automatically fires.

I can't tell this solution is stupid, ingenious or completely fucking psychopathic, either way the prisoners aren't leaving.