An identified patron advised the station agent at the Montgomery Station that there was a subject in the lead car of a Millbrae bound train who spoke about explosives and blowing up the train. The train was held at the 16th St. Station while SFPD and BART units converged to that location. Trains were held out and the train and station was temporarily evacuated and closed. SFPD bomb dogs responded and searched both the trains and platform with negative results. SFPD officers detained a subject who matched the description on the street level nearby the station. Officers made contact with the original party but she stated she would not be able to respond to the station. Further investigation revealed that the suspect was mentally unstable and a danger to others. The suspect was transported to the SF General Hospital for psychiatric evaluation. The station was reopened and trains released at 1611 hours; resulting in an approximately 50 minutes. Notification was made to TSOC.