On a recent July afternoon in The Bronx, 19-year-old Franklin Mesa went up to Nathaniel Rivers, 35, who had just parked his car, and allegedly stabbed him to death in front of his wife.

Mesa’s family members described him as schizophrenic. Police said he was arrested last year for punching somebody, twice, in the face. And a neighbor told The Post that he was often the source of “hostile, aggressive” situations, including preventing a woman from getting on the bus...........