Stephen Sackur talks to veteran, often controversial, civil rights campaigner Al Sharpton.

One of the bleaker themes of Barack Obama's presidency has been the crisis in relations between black America and the criminal justice system. Recently, unarmed black men have been shot dead by the police and officers were gunned down in what appear to be acts of vengeance.

A new movement, Black Lives Matter, has given voice to anger on the streets. Who speaks most effectively for black America today? Show less