Check out the full length 1970 Documentary "Gimme Shelter" chronicling the last weeks of The Stones' 1969 US Tour which culminated in the disastrous Altamount Free Concert.

At the Altamont Free Concert the security was provided, believe it or not, by the Hells Angels. Armed with pool cues, and as high on drink and drugs as the audience was, the mood quickly turns ugly. 

A young man, Meredith Hunter, was actually stabbed and died after trying to get onto the stage during The Stones' performance. 

Gimme Shelter - It is something you have to see to believe.