The United States Justice Department will not prosecute the former police officer who shot dead unarmed black teenager Michael Brown in Ferguson.

The ruling on 4 March comes after Darren Wilson was exonerated by a Missouri grand jury in November 2014 over the shooting, which he claimed was in self-defence against the teenager who allegedly struck him in the face and tried to grab his gun.

The 18-year-old's death sparked weeks of protests across America. Wilson later went into hiding and resigned from his post when he was cleared of murder last year.

But federal officials did rule in a separate report that black people in Ferguson were subject to a disproportionate level of "excessive police force" by police including "baseless traffic stops", according to AP.

More than 24 recommendations were made to integrate the police department and court system, including training officers to quell confrontations and improving its recruiting and promotion procedures. City officials were said to be cooperative to the changes proposed.

"It's quite evident that change is coming down the pike. This is encouraging," said John Gaskin III, a St Louis community activist. "It's so unfortunate that Michael Brown had to be killed. But in spite of that, I feel justice is coming."