Additional charges are expected to be filed against the man who wielded a loaded shotgun near the Capitol on Jan. 18 after authorities discovered more hazardous materials in his vehicle on Friday.

Capitol Police investigators were conducting a follow-up search on Feb. 8 of the green pickup truck driven by Michael Gorbey on Capitol Hill when they discovered “hazardous material” in the vehicle, police spokeswoman Sgt. Kimberly Schneider said.

Police evacuated the immediate area surrounding the truck and neutralized the device, which turned out to be negative, Senate Sergeant-at-Arms Terrance Gainer said.

The vehicle had been stored in a parking garage at the Government Printing Office. According to a Capitol Police officer familiar with the case, the device was initially radioed into police headquarters as a “plastic device with wires and black powder.”

Gorbey already has been charged with one count of a felon in possession of a firearm. He has pleaded not guilty to those charges and is expected back in D.C. Superior Court court for a hearing on Feb. 14.

— Elizabeth Brotherton and Jennifer Bendery