Rampage
(2009)

Bill's massive killing spree was also a pretext to commit robbery; the money he burns in a public demonstration was fake.

He kills his best friend, a known radical, and makes it look like he did the killings and committed suicide.

Bill gets away clean until his friend's father claims on the news that Bill is the killer; he grabs his money and disappears.

The home video we see of him throughout the film where he expresses his psychopathic views and takes credit for the killings is posted on the Internet 2 years after the events; in it he reveals he will do it again in other cities.   

Thanks Fleetwood!