He also says he believes five shots were fired into the vehicle.
Attorney Michael Sussman said Wednesday he doesn't know if gunpowder evidence was intentionally removed. But he says 20-year-old Danroy Henry's car wasn't maintained properly after the shooting.
A spokesman for the Westchester County district attorney's office won't comment.
The Pace University student was killed Oct. 17, when two officers fired at his moving car. Police had been called to a disturbance that spilled out of a bar in Thornwood, 20 miles north of New York City.
Henry was from Easton, Mass. His killing has engendered differing accounts from police and witnesses.
