Capitol Police arrested a staffer for Sen. Cory Booker who was carrying a gun Monday evening, as the New Jersey Democrat kicked off a marathon “filibuster” in the upper chamber.

Police said “a member of Congress” they didn’t identify helped an aide to Sen. Cory Booker bypass security screening. The aide later informed Capitol Police he was armed.

A Senate staffer was arrested for carrying an unlicensed gun in the Capitol earlier this week, Capitol Police said Tuesday. It was the latest in a string of incidents in which a staffer or member of the public has gotten into the Capitol or an office building with a weapon.