A man was arrested on suspicion of carrying a concealed weapon after police found him outdoors — naked — and he told them he had a tool in his rectum, authorities said.

The man was lying on a tree stump, masturbating beside a nature path, near a Bay Area Rapid Transit station Thursday, police said.

John Sheehan, 33, of Pittsburg, was initially arrested on suspicion of indecent exposure. But when asked whether he was carrying anything police should know about, Sheehan mentioned the tool, said El Cerrito Detective Cpl. Don Horgan.

“You can’t get much more concealed than that,” Horgan said.

Officers drew their weapons and firefighters were called to the scene. Sheehan removed a 6-inch metal awl wrapped in black electrical tape without incident.