I'm currently trying to complete the "Kill Marowski" quest and it's infuriating!
I have the level 3 Sandman perk. I've tried every type of weapon. As soon as he's asleep, I sneak into his room and try to V.A.T.S. his butt. Every time his health hits 0, he sits down for a few seconds (during which time the residents have turned hostile), and then stands back up with full health.
Anyone know what's going on? Is it a glitch? Am I doing it wrong?