A Remington 870 Sawed-off Shotgun was owned by the Manager of the Gotham National Bank.
During the Robbery of Gotham National Bank, the Manager retrieved his shotgun from under his desk, fired it through a window and into Chuckles' back, which killed him. The Manager then casually fired off several shotgun blasts at Joker's Henchmen. Grumpy asked Bozo if the Manager had run out of ammo, but was tricked into believing so. The Manager then discharged his shotgun into Grumpy's shoulder, then discovered that he was out of shells and Joker shot him in the shoulder.
The Joker later kept that shotgun for himself and used it frequently until his capture by GCPD SWAT. One notable use of Joker's Shotgun was announcing his presence by firing up into the air during Bruce Wayne's Fundraiser for Harvey Dent, as well as intimidated some of the party attendees by pointing a shotgun at their faces.
It was last seen being used by the Joker to shoot at a police officer, and later an armored SWAT truck housing Harvey Dent, who was being transported after publicly claiming to be the Batman. He was not seen using it again, and was likely left inside the overturned semi-truck.