The frantic call for help came from a college student who worked as a summer intern. She’d gone for drinks at a local bar with a co-worker. A celebratory night took a dark turn when she got into his car for a ride to the train station.

“Caller is a female, says he put a gun in her mouth and sexually assaulted her,’’ the 911 dispatcher announced over the Boston police radio system just after 10:30 p.m. July 26, directing officers to South Station.

“We’ve got the victim,’’ an officer radioed back after locating the 21-year-old woman at a train terminal, according to audio of the transmissions recorded by Broadcastify. “I got the suspect’s name. It’s Jamie Clarke . . . he’s an investigator with the IRS.’’