When you finally get to Bohan, the chase will slow down a bit. Keep an eye on everything going on around you.
Certain things will always occur in the pursuit, such as trucks losing their cargo in the road, cars swerving and the like. You're going to be chasing him for a good long while. Naturally, you don't want to let him stray too far, or you'll fail the mission automatically, but understand that this guy is going to take you on a true excursion through the city. When Rivas makes his getaway, follow him on your HUD. Having your own car ready to nearby will make your life a lot easier. Get out of the car, whichever one you're in, but leave it as near to the building's entrance as possible, since you're going to go in, try to find this guy, and he's going to run off and speed off in a car. Head to Asparagus Avenue from whatever location you happen to be from (since it will vary depending on where you stole the cop car and ultimately lost the cops). You can then abandon the cop car for more inconspicuous, less destroyed vehicle. Have the computer send the information to your GPS. You'll find out that he hangs out in Broker (more specifically, on Asparagus Avenue). You'll be told to access the cop car's computer (which can be done following the on-screen prompts) and to look for a guy named Lyle Rivas. When you've lost your wanted level (which could be a bit of a challenge considering you're in a cop car and probably have killed some cops to get it), Niko will call Brucie and the next leg of this mission will begin. We'll leave this part up to your imagination, but once you get a cop car and it's in good shape, make it your absolute top priority to lose the heat so we can continue. But chances are you'll have to mess with a cop, and maybe even kill one or two, to get a cop to abandon his car long enough for you to jump in it. You may be lucky enough to find a cop car parked on the road with no cop cars around, in which case you can simply break in, hotwire the car, and be off. You've likely stolen a police car or two by this point in the game, so you'll understand fully that it comes with incredible risk.