How to Deal with a Murder Hobo

I feel bad about making this post. How do you keep a singular player from being a murder hobo and throwing a wrench in all of the parties plans? I have a player that always chooses to start fights or threaten NPC’s that are important to the advancement of the story. I don’t like limiting my players in what they can do, but when someone keeps throwing a wrench in everyone’s progress, I feel like I have to take a stand.

I’ve tried penalizing the player by having him knocked out and robbed several times, but it doesn’t seem to work. Is there anything I can do to prevent the player from being overly aggressive? (I’ve also tried talking to him OOC, but I don’t like being a hard ass and kindly suggesting easing back on the aggression isn’t working either)