This is Bob the cop. He's going to arrest the pyrokinesis user for some crime he apparently commited.
If the pyrokinesis user kills Bob, then DanielB's answer will likely soon follow. If the pyro keeps Bob alive and "just" hurts him to keep him away, for example by reaching for the electricity in Bob's taser and using that to tase Bob, then friendlier methods to arrest him and place him in an asbestos cell somewhere will be taken.
The pyro has to take on society. Is he going to steal his food every day by force? Or the money to pay for his house and livelyhood? What is he doing for social interaction? Even if he just gets a job and does the normie thing, as long as he's wanted enough that he comes into contact with the law, he is screwed.
So sending Bob didn't work? Ok the police can simply hire someone to change the locks on his house while he is away, and if necessary empty the house and use that as a bargaining tool to get him to cooperate with justice. Doesn't work? Ok next time he turns the corner to his house he gets blown down by a watercanon, by the time he knows what is going on he's in handcuffs with a hood on, cold, wet, disoriented and halfway to a cell. Or maybe the police does the time-honored act of lifting him off his bed in the early early morning, since this is a powerful individual they might also send some teargas inside every window just in case. Or maybe they just wait for him at his commute where they tase him (cant control it if it happens before he reacts), pepperspray him, fire tear gas and a rubber bullet or two into his chest to incapacitate him as he rounds a corner and arrest him...
Unless the pyro is a hobo who keeps moving and tries to stay out of sight, there just isnt a good way the pyro can truly stay ahead of the law.