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Described as the most boring criminal ever, Ralph is a bad boy all the same. He's laying low in a quarry (as you do). You can either snipe him from higher ground, or get in closer and spook him. In that case he'll jump in his 4x4 and drive off. Ram him off the road and he'll give up.
A man close to Trevor's heart, Larry Tupper is a meth dealer with a violent streak. He's also hanging around with some miscreants who will try to protect him if you get up close. They're loitering outside a barn, check the map for the exact location.
Glenn is a badass banker up on top of Mount Chiliad. Shooting him from distance is easy enough. If you get in close Glenn will jump off the mountain (with a parachute, he's bad but not crazy). There's another parachute on the ground nearby, so pick that up and give chase.
Curtis Weaver (aka Father Christmas) is a nutjob of undisclosed crimes. He's living off the grid, in some kind of hobo camp up north. Hunt this poor old guy down, so you can feel like a big man. Like the others, Curtis will try to run, but fortunately he doesn't really have the legs for it any more.
So Trevor has found himself a bail bonds employment opportunity, working for the lovely Maude. These bounty missions involve tracking down known felons using sketchy map info. This isn't easy, so check out the exact locations on the map above.
These targets can be hounded into submission by chasing them down and threatening them. For a swifter application of justice you can just stick a bullet in their heads, but the payout for a dead criminal is less.