When Carmona's men are attacking the PMC, after you destroy the tanks, set a charge of C4 on the gates closer to the mansion, and detonate it. It should drop straight down and block the road leading out of the compound. Enter the mansion, and trigger the intermission sequence. When you exit the building, the road leading out of the compound will still be blocked. Kill Carmona's bodyguards, and his jeep should be stuck in the rubble of the archway. Kill him, and snap the picture for easy verification of Carmona.

When completing the mission on the oil rig in the water behind the PMC, kill Blanco and take his weapon, the hunting pistol. The hunting pistol is a very powerful weapon, often killing enemies in one shot. With the hunting pistol in your possession, continue through the "Finding Solano" mission. After the encounter with Carmona inside the Villa, he will run in a straight line directly away from you, giving you a clear shot at his back. If you miss on the first shot, he has a good bit of a jog until he reaches his jeep, giving you plenty of time to gun him down.