Is he supposed to assume that all of them have murderous intent?

Hmm yes? He should at least assume that they could be dangerous. How could Batista rule out prater when he knows that Dexter hunts down serial killers?

he was put into a precarious situation and was trying to fight his way out.

I just don’t buy the fact that in such a precarious situation you turn on the one person in the room that is not actively threatening your life and has actually freed you.

EDIT: word