Two off-duty federal law enforcement officers detained an armed man on the D.C. Metro near Ronald Reagan Washington National Airport during the Monday night commute, according to a U.S. Customs and Border Protection press release issued Tuesday.

A female U.S. Border Patrol agent had been traveling on the rail’s Yellow Line when she witnessed a fight break out between two people in the adjacent car. The victim in the fight tried to escape the attacker by fleeing to her car. That’s when the unnamed Border official took action.