If the guy turns up dead after release, the po-po will be eyeing him mighty hard anyway. Maybe if he goes public loud enough, he can cast suspicions elsewhere if the the guy bites it.
Just a thought.
Edit: Heck, there are 50 possible suspects here alone.
Yeah, and he'll be eyed all the more quickly since being a blabber mouth about it.
All I know is if I was ever (God forbid) motivated to the point of homicide I'd
1. Have a damn good reason.
2. Would not speak or write about it, even to myself.
3. Would seriously train and prepare, potentially for months or over a year.
4. Would buy everything for the one time use only, after which it would be burned/permanently disposed of.
5. Would put the Navy SEALs to shame in its execution and would leave zero implicating evidence.
And I would make sure it was cold. Granted the odds of my ever encountering a situation that motivates me to this extreme are thankfully minimal, but if you're going to carry it out you do it right and for the right reasons (revenge is secondary). And you don't sink to their level like the torture options a lot of people run their mouths about. That's where you mess up and that's where, instead of contributing something positive to the world, you get caught and end up in prison for the rest of your life, yet another drain on innocent taxpayers.
The problem with vigilante justice isn't the theoretical concept, it's that the people who usually try to carry it out aren't strong enough to do it correctly and are in it for revenge and attention as opposed to any rational notion of justice or public service.