Make sure you've got a fast car and you can drive it like you stole it.
Objective: Take out the fixer
Objective: Escape the Police
Before starting this mission get yourself a car you're comfortable with and make sure it's fast too. Get it parked at the bottom of the stairs below the waypoint.
Once the cutscene has played out, get in the car quickly so you don't get ID'd. If you're quick enough you can just head straight over to the waypoint. When you reach the spot chase down the van and deal with the driver. Take care of him quickly and the police will being to show up, so put your foot down and escape the po-po to complete the mission.