Do NOT drive through the blockade and go up the steep slope. If you do, you take a super long circular route. You go through a series of hairpin turns up and around Mount Chiliad. You're soon up into the fog and mountains. Eventually you get around to the house. If you go left at that fork, it's a much shorter route.

Either way, you need a photo of him in one piece. When you get there, there are a few cops out front. Shoot at least 2 to get their SMGs. When you shoot them, the snitch leaps into a car and drives off. Now you are chasing him on a motorcycle on the windy roads - and with you SMG you can shoot straight ahead of you which makes it super easy. Just empty the guns into him until the car catches on fire. He'll jump out, kill him, and take his picture.

Then return to the trailer park spot.

Mission Passed

You get 2 phone calls immediately afterwards. One is from Cesar. He says he's taking care of your sister. He says he'll send a cousin out to help you out. Then another call comes in from Sweet - he's in prison and is upset. He hangs up pretty quickly.

Note if you run straight out of the trailer park and down two alleys, there's a bouquet of flowers there!

Note 3 - when you get back home after this, all your territories are gone.

Grand Theft Auto San Andreas Walkthrough