Filmmakers Mike Gray and Howard Alk arrived at the crime scene a few hours after the massacre to document the scene. Their footage disproved official police testimony and newspaper accounts which portrayed the raid as a "shootout" with the Black Panthers when in fact it was nothing short of a deliberate execution.
This footage was incorporated into their documentary, The Murder Of Fred Hampton, which is available in a newly restored version on DVD. Here's the lower resolution online version:
The police involved in the raid, State's Attorney Hanrahan and the FBI officials involved in the conspiracy against the Black Panthers were never brought to justice. However, survivors and the families of the deceased eventually won a civil law suit more than a decade after the murders thanks to the diligent efforts of the People's Law Office in Chicago.
One of the lead attorneys, Jeffrey Haas, has recently written a book on the case, The Assassination of Fred Hampton. It's a great read and much-needed reminder of the consequences of unbridled government power which is as relevant today as it was in 1969.