Ashley Stewart, KING 5 News

SEATTLE -- Seattle police arrested a 31-year-old man during Monday's Ferguson protest after officers discovered a cache of weapons, ammunition and explosives in his backpack and car.

Jeffrey Alan Acord was booked into King County Jail. On Monday, he was charged with possession of a concealed weapon without a permit, carrying a dangerous knife and illegal possession of fireworks.

A bystander had notified police after witnessing the suspect reach under a vehicle with a road flare during the demonstration. Police say Acord was carrying a loaded handgun without a permit and a 7-inch knife, and officers found a box of ammunition, an assault rifle, a shotgun and a box of large fireworks in his car.

Five people were arrested during the Ferguson protest in Seattle, but only Acord faces weapons charges.

Seattle police say they're looking for a second man who threw an improvised explosive at officer during the demonstration, filmed at 1:55 in the video below. (Warning: Video contains explicit language.)