I am having a hard time understanding why you consider the wallet and keys left on the bridge evidence of murder or details suggesting murder.
To me this is showing that he was trying to make it easier to identify his body and make it easier for his parents to collect his car.
If you have any links to news articles explaining murder theories please post them.
Imagine there are OTHERS who wanted to kill him for his allowing films to be made of their sessions, or that there are OTHERS who wanted to kill him because he was not as "exclusive" as he was leading them to believe.
They come and escort him to the river ~ and one of them grabs his keys and wallet off his student desk!
They simply tossed him in the drink before they put his wallet and keys into his pocket, so they left them behind before they got caught with them.
The cops are no doubt evaluating all the evidence in that light.