The area has since been taped off. Crews were still clearing it out Friday morning, Nov. 22; countless items were found inside, including four guns. 

Milwaukee County Sheriff Earnell Lucas identified the man as 41-year-old Geoffrey Graff.

Authorities found the bunker after they received a shots fired call. Once at the scene, they say Graff told them he shot rounds into the river because he was mad his dogs ran away. He was then taken into custody. 

"They [officers] discovered a concealed entrance to an underground encampment," Sheriff Lucas said. 

In the eight-foot deep and 20-foot long bunker, authorities found four guns, three knives, a bow, grill, generator, propane tanks, and food. 

Sheriff Lucas said Graff could've been living there for years. 

"Obviously it required some ingenuity for an individual to do something of this nature in, literally in an urban area, an urban setting and it go undetected for any period," he said. 

"One would wonder how in an urban setting an individual is able to hide in plain sight, if you will. It's all of our responsibility to stay vigilant, and if you see something say something," Sheriff Lucas said. 

Graff is in custody and faces charges of second degree recklessly endangering safety and possession of a short-barreled shotgun. An investigation is ongoing, but authorities say they don't believe his actions were politically motivated. 

Milwaukee Area Technical College owns the land Graff's bunker was found on.