I must be getting old...

[Worbah]

I've done the mission for Tanya a dozen times before, the one where you have to stage the suicide of Pedro Nunez. Somehow I've managed to forget how you're supposed to do it. I go up to him after 00:00, ask for his pistol with no one around, and pop one to the back of his head. He dies instantly, but somehow it initiates combat with the natives. What am I doing wrong?