Original sentence: Perhaps one of the most notorious events in Hells Angels' history involved the December 6, 1969, Altamont Free Concert at the Altamont Speedway — partially documented in the 1970 film Gimme Shelter — featuring Jefferson Airplane, The Flying Burrito Brothers, and The Rolling Stones
Edited sentence: Perhaps the most notorious event in Hells Angels history involved the December 6, 1969, Altamont Free Concert at the Altamont Speedway — partially documented in the 1970 film Gimme Shelter — featuring Jefferson Airplane, The Flying Burrito Brothers, and The Rolling Stones