Upon arriving at the Unknown Contact mission start point, you'll find out it's Francis McReary. He tells you he knows you killed Mikhail Faustin and that someone is trying to blackmail him with some photos. He needs you to find this guy and get the photos back.
Grab a vehicle and head to the viewpoint off Union Drive East. Once you arrive and watch the short cutscene, you'll be told to call the blackmailer. He has his phone on him, so you'll know which one is the blackmailer by watching which people answer their phone. As it happens, the guy you need to find will be wearing a jacket with a yellow hood. He should be sitting on a bench near the hot dog guy.
Find him and move down closer to him. He'll tell you to call him back when you have the money. If you've found the right guy, call him back straight away and after a short conversation, he'll try to escape on foot. Gun him down and grab the photos, then you'll be awarded with a 2 star wanted level. You need to lose the cops, so sprint back up to the road and find a vehicle. Do whatever it takes to lose the cops, then you'll be told to take the photos to Francis McReary. Make your way to his apartment and deliver the photos.
- Once you figure out who the blackmailer is, try sniping him from a position up near the road. He'll drop the photos, but then you can take a car and lose your wanted level. Once you've successfully lost the cops, come back and pick them up. Simple!