An officer was flagged down at the station on a report of a man possibly in possession of a gun. Officers detained a male subject who reportedly had the weapon, but did not have one on his person. Two victims told officers the man threatened them while on the train by telling them he had a gun in his possession. A warrant check on the subject revealed a felony no-bail arrest warrant for robbery out of San Mateo County. The subject was placed under arrest and booked at Glen Dyer jail for threats to persons and the warrant. TSOC notified. 1109-3320 L12.