The gun used in the shooting hasn't been recovered, sources said.
Police believe the shooter used a B&T Station Six, known in Great Britain as a Welrod pistol, according to police sources. The gun doesn't have a silencer but does have a long barrel that enables the 9 mm to fire a nearly silent shot. The gun requires manually cycling ammunition from the magazine.
The weapon is not easily attainable so investigators have been running down all recent purchases, according to police sources. NYPD detectives arrived Thursday at a gun shop in Connecticut that sold a weapon of the same type, sources said.