It started with a Twitter message on Sept. 19: “Roommate asked for the room till midnight. I went into molly’s room and turned on my webcam. I saw him making out with a dude. Yay.” That night, the authorities say, the Rutgers University student who sent the message used a camera in his dormitory room to stream the roommate’s intimate encounter live on the Internet. And three days later, the roommate who had been surreptitiously broadcast — Tyler Clementi, an 18-year-old freshman and an accomplished violinist — jumped from the George Washington Bridge into the Hudson River in an apparent suicide.