Geoffrey Graff.

MILWAUKEE (AP) — Authorities say a man living in an underground bunker with a stash of weapons along a Milwaukee river had been there for a “considerable period” but it’s unclear for how long.

The Milwaukee Sheriff’s Office on Friday identified the man they arrested Wednesday as 41-year-old Geoffrey Graff. Sheriff Earnell Lucas says Graff came to their attention when residents reported shots fired in the area.

Lucas says when officers found the bunker Graff immediately incriminated himself by saying he had fired the shots into the river because he was angry at his dogs for running away.

It’s not known whether Graff has a lawyer.

Lucas says the bunker was 8 feet (2.4 meters) deep, 8 feet (2.4 meters) wide, and 20 feet (6.1 meters) long. Officials say inside they found two shotguns, a pistol, a long rifle, and a bow and arrow.

Milwaukee prosecutors are considering charges.