A BART system service worker reported that a male suspect brandished a knife at him and went back up to the platform. The suspect was located by officers and a sergeant, detained at gunpoint and taken into custody without incident. The folding knife was also recovered. The victim identified him as the responsible person and placed him under citizen's arrest for brandishing a weapon. A lieutenant responded to conduct a use of force investigation. The suspect was issued a prohibition order before being booked into the Santa Rita Jail for brandishing a weapon. BART Central was notified of the incident. TSOC was notified.