Martinez is on the roof, and he’s guarded by lots of henchmen. To get up there you need to get to the front gates that lead over a bridge to the roof. Use the scope on the agency rifle to take out gang members at a distance, minimizing the harm that can be done to you. Remember, if your shields are depleted, make a run for it! There’s nothing wrong with cowardice in our book. Your shields will soon recharge and you can have another go at it.
After you’ve taken care of Martinez, gang members will be out for your blood. Climb up the balconies to the new safe house that’s appeared on your map to make a quick getaway. Get in an agency car and take out the gang members outside the agency until you get new info.
The best way to tackle Guerra is to attack his building from the front. Go to the left of the building where it’s built so you can jump it. He’ll either be at the top of the building in the sheltered patio, or a couple of levels down. Either way, try and focus on him before his whole gang manages to catch up with you. Throw grenades, but try and keep him penned in a corner, so he can’t run away when you do throw one. Remember to jump and move, as this builds up your agility, allowing you to jump higher and run faster.
Get an Agency supercar and head for the right bridge to the other island. The left bridge means you have to jump off without a car if you want to get inside the complex quickly. After you’re on the other side of the right bridge, head left toward the front of the complex and head in. Keep driving around until Diaz makes himself known on the floor. Keep running him over until he’s dead. If he doesn’t get out onto the floor, you’ll have to get out yourself and try and find him by going up the stairs next to the garages. It’s best to stay in the supercar here, as it’s well armored and can’t really be touched by other vehicles trying to ram you.