More than six years ago, police officers shot and killed Kevin Cerbelli, a mentally ill Queens man, after he barged, shirtless, into a Queens precinct station house brandishing a screwdriver and a knife.

Now, as a lawsuit filed by Cerbelli's mother, Loretta, inches closer to trial in federal court in Brooklyn, new questions have emerged about the procedures police employ in more than 50,000 encounters a year with emotionally disturbed people.