Maniac is a 1980 cult horror slasher/splatter directed by William Lustig and is notable for character actor Joe Spinell's portrayal of a psychotic serial killer Frank Zito as well as incredible special make-up effects by genre cult guru Tom Savini and neo-noir dark romantic depiction of New York.
The following weapons were used in the movie Maniac:
Frank Zito (Joe Spinell) uses a 12 Gauge Double Barreled Shotgun in the most famous scene of the movie, where he shoots disco boy (special effect makeup artist Tom Savini) and disco girl (Hyla Marrow) with it in their car. Zito uses a violin case to illegally hide his weapon, when he's in the city.
Unknown sports or air pistol
Frank Zito uses an unknown pistol held in special case, while practising shooting in his apartment. He doesn't fire this pistol in the movie, but there are bullet holes in the wall, presumably by bullets fired from this pistol.