This mission is given to you by Lester ("L" on the map) and can be started by Michael. Steve Haines needs you to go into the FIB building and get some "evidence" to clear his name. When you gain control, get into the car with Lester and drive to the FIB building. He'll mention on the way that you're waiting for a janitor to leave, who you will get over onto your side, allowing you access to the building.
Park outside of the parking garage and everytime a vehicle comes out, zoom in onto the license plate to check the number. Keep doing this until the guy you want comes out, who you will need to tail. As you're following him, make sure you stay far enough away to not spook the guy or let on you're following him, especially since he will make plenty of stops at lights.
Once he makes it to his apartment, wait a little bit and then follow him inside. You'll grab the goods, so get back to your vehicle and then head back to the garment facility to finish the mission.