Here's what you need to kill him:
Reputation with Conrad Marburg: -4 Answer blue/Suave at every chance with him, and save Madison.
Dossier on Marburg: 66% This is where I was when I got it. Lower might work. Buy the Intel relating to him, and before saving Madison, go to the right, there's an (easy) lock on a door to your left. Inside is a dossier on him. That'll get you to at least 50%.
Razor Wit: Answer Blue/Suave for the entirety of 10 conversations. Self-explanatory. Heck in Taiwan and Gregori in Moscow are both easily accessed and respond well to full conversations in Suave. Your first conversation with Marburg can count towards this, and I assume your second can as well. You'll want it before entering the museum.
You'll get the perk "You talking to me?" once he's been provoked, and the trophy once he's down. Enjoy.