This has the same setup as the Fugitive Wanted achievement. By having another racer hit a cop car/ambulance/fire truck repeatedly, you'll have a phone call to which you can either accept to be part of the chase to help catch the outlaw.
Once 2 or more of you have accepted, the race will begin after the clock has counted down. Try and keep up with the outlaw, crashing into him at any time. Once you are close enough, you can hit to charge an EMP which will disable his power. Hitting will begin charging the EMP and will charge fully if you stay close enough to the outlaw. If you lose too much distance to the outlaw, the charging of the EMP will stop and you'll have to charge it again when you get close enough.
You have 2 minutes and 30 seconds to catch the outlaw before they have escaped.