In addition to the summary and articles I compiled, I also wanted to add my thinking after following this closely for a while:
I see these as the most likely two broad options:
1. Brian intentionally left through an unusual exit--either he jumped the balcony outside, he left through the back exit by the movie theater (and the camera failed to capture it), or he somehow accessed and left through the construction area despite it being difficult to reach and the doors being chained. There are multiple reasons I can think of that he might have chosen to leave this way. These are all just based on speculation. Perhaps Brian was trying to avoid someone he had trouble with inside, perhaps he was discreetly meeting up with a romantic interest, perhaps he was meeting someone to score some weed, perhaps he planned to go to another location such as an after-party with a friend, an Ugly Tuna staff person, or band member. Upon exiting, Brian somehow got into a situation where he was harmed or accidentally fell into harm (an accident or overdose?). People who met him or who were with him hid his body. Less likely: By his own doing, Brian fell into the river or some other remote/hidden area and his body just hasn't been discovered yet.
2. Brian met with foul play or a medical issue induced by being over-served or overdosing on a substance while still inside the bar after hours. In the 24 hours that followed, someone (bar staff, band, building security etc.) hid his body inside the building or, more likely, somehow got it out of the building and disposed of it somewhere remote where it hasn't been found.
I think there's a chance Clint has some sort of additional information (perhaps he and Brian had a conflict that night or he and Brian used drugs together etc.) If he does know something, he still might not know what happened to Brian altogether, but might know it is related to some sort of secret they shared together that could also impact Clint's reputation as a medical professional. I've never met anyone involved here, but it says something that multiple people--Brian's Dad, Alexis' Dad, Alexis, and Brian's brother, Derek-- all seemed to think Clint might be holding back important information. Clint hired a lawyer and refused a polygraph. In these forums, it was said he requested immunity in exchange for sharing information, but was refused. I've never been able to confirm the request for immunity.
