A patron reported to the station agent at Orinda Station that a man on the SF Airport bound train was acting strangely and was in possession of a handgun. The train was intercepted at Rockridge Station. The suspect was described as a white male in his 40's, bald, wearing a pink long sleeved shirt. Officers responded and located a male matching the suspect description near the agent's booth. The man was detained and admitted to having a replica gun in his bag. A search of the man revealed the replica BB gun in his bag, as well as a syringe of suspected heroin. The man was arrested. The man told officers he had just bought the BB gun and had taken it out to look at it on the train. Officers determined that the name the man provided was false and they confirmed his true identity. Record checks showed that the man had an outstanding no-bail arrest warrant for burglary, held by the San Mateo County Sheriff's Office. The man was booked at Glenn Dyer Jail for possession of narcotics, possession of a replica firearm, providing false information to a peace officer and his outstanding warrant. There was about a ten minute delay in service as a result of this incident. TSOC notified.