They probably don't ever think that far considering they hate living and aren't so much interested in doing the best thing.

He probably wants to die but is too scared of any of the real difficult survival instincts you have to fight against while you're body is trying to stay alive. Therefore he thought a quick shot from a police officer whose job involves certain difficult decisions would be better than the other "easy" methods of suicide. When you're not rich enough to have a garage to die of carbon poisoning you don't have many great options other than that stupid telephone number where people tell you that "you should like living so stop feeling bad" which doesn't fix or help anything.

He most likely assumed that police would wrongfully shoot a black man but he didn't expect them to be trained well enough to assess the situation involving a "black male holding a knife" in split second decision timing.