In 1969, Jerry Garcia and his Grateful Dead bandmates, booked to play with the Rolling Stones at the Altamont Speedway outside San Francisco, suggested that the Stones hire members of the Hell's Angels motorcycle gang to act as security guards during the show (in exchange for $500 worth of beer). The concert ended in tragedy when a young black man was beaten to death... by the Hells Angels!
Where were the Dead? Ironically, they had decided not to perform. They did, however, cash in on the violence -- composing a song ("New Speedway Boogie") about the deadly show.