Ahh, that's a tricky one. You are supposed to wait until night and he'll appear at one of the entry points. I'm not sure if it's the same day as the mission is given or the day after. In the town of Sagrada there are a few NPC's that are called "Local". They are not normal civilians, and once you kill Gonzalo Teteira they'll turn hostile. If you kill them, there are 3 or 4 of them, before Gonzalo arrives, he will be hostlie when he gets there.
Here's what I do: When given the mission I go to Sagrada and kill those Locals. I then exit to the global map and speed up time. When Gonzalo arrives you'll get a message that there is fighting going on, re-enter the tactical map, locate and kill Gonzalo and Bob's your uncle
