Laquan mcdonald video
Police radio recordings reveal officers repeatedly requested Taser backup.
The Chicago mayor took "responsibility for what happened."
Chicago police maintain they had nothing to do with a mysterious gap in the footage.
Brandon Smith says he kept pushing, even after his FOIA request was denied.
WHAT'S HAPPENING
Jabari R. Dean, 21, of Chicago, threatened to kill 16 white male students or staff at the school.
Jackson called for "bold comprehensive change" in the Chicago PD and in the criminal justice system.
City officials have framed the cop who killed McDonald as one bad apple, but the department has been rotten for almost a century.
The president said he was "deeply disturbed" by video of Laquan McDonald's killing.