Head on up to the top of Mount Chiliad using the gondola service. Go over to the right and move along the trail. Look around the edges to find your target, Glenn Scoville. He is about to Base-jump off the mountain, and do so to escape Trevor. There is a parachute by the dirt bike. Grab it then jump after Glenn. Deploy it and come in for a landing after Glenn. Pull out the Stun Gun and shoot him to bring him down. Just get close to him and Trevor will knock him down (If you're going for a live capture). Otherwise just shoot him with any other gun and he's dead.