And now, here's the footage of Brian leaving:
There isn't any. The police located footage of Clint and Meredith leaving dazed and confused at 2:15, but the only footage of Brian comes when he briefly exits to talk to two women outside ... and then turns around and walks back in.
In all the years that his family has been searching for him, no one has ever managed to explain how Brian disappeared. Did he slip out the back? No, the police checked the camera overlooking that door. Could he have blended into a crowd of people? It's possible, but that doesn't explain why he wouldn't return home, especially given that he was planning to propose to his longtime girlfriend the following week. Was he murdered by another person in the bar? It's unlikely, especially given that they would've needed to dispose of the body right then and there (without being spotted on any surveillance cameras), because the police searched the bar soon afterward.
Two years after Brian's disappearance, his father Randy died in an accident. In the comments section of his online obituary, a message stating "Dad, I love you. Love, Brian (U.S. Virgin Islands)" was posted. Police traced it, only to find it had been posted from a public computer in a nearby county.