WASHINGTON, Oct 30: Police shut down a US Congress office building on Thursday to search for a man believed to be carrying a gun in his backpack and a woman accomplice, police said.

But it turned out that the alert was apparently triggered by a fake gun.

The Cannon office building was shut down and evacuated after a man and woman passed through a security checkpoint with what appeared to be a revolver in a knapsack. Police said it was in fact a fake gun and a Halloween costume.

The man, described as a white male of about 20 years of age, put his bag through a metal detector upon entering the Cannon Office Building, a police spokesman said.

Security officers saw something that looked like a revolver and moved to question the man, but before guards could stop him, the man grabbed the bag and ran into the building.

Jessica Gissubel, a spokeswoman for the US Capitol Police, said police were also on the lookout for a white female believed to be in her 20s.—Reuters