Dispatch: Ofiicer down on 16th. Backup needed.
Cop1: How many times did I swear
Turpin wouldn't seal the deal? (Take a guy's life?)Pay up.
Cop2: Yeah.
I would need more context, but if Cop2 thinks that Turpin is a killer, then yes, kill someone.

Seal the deal means to make a deal official.
Well you can't actually tell because there's just one scene of those two cops.
The just hear on the radio their colleague is down and needs backup.