@thtgiang
Yes, because there's no possibility of this guy getting out, he 100% poses no threat now or in the future and posses no weapons and poses no threats should he escape, sure. That's totally the implication here; the muzzle was the correct analogy, not yours. He's still a threat if he gets out, just like if the dog gets out of the muzzle.
Keeping him around is falling into the trap dude. Especially considering, as I just said, there's no proof he's worth keeping around, and even finding out isn't worth it considering what just happened. You guys are the kinds of guys that would die real quick because they think they avoided the traps but really walked into them head first.