A night-time car chase in Cleveland that ended on a schoolyard where more than 100 shots were fired at the suspect's vehicle appeared to be over when an officer opened fire again, a prosecutor said in announcing charges against the patrolman and five police supervisors.

Cleveland patrol officer Michael Brelo stood on the hood of the suspect's car and fired at least 15 shots through the windshield – five fatal – at the two unarmed people inside, Cuyahoga County prosecutor Tim McGinty said Friday.

McGinty cited a US supreme court ruling this week that said police can't fire on suspects after a public safety threat has ended. He said the other officers on the scene had stopped firing after the November 2012 chase ended.

"This was now a stop-and-shoot – no longer a chase-and-shoot," McGinty said in announcing two counts of manslaughter against Brelo. "The law does not allow for a stop-and-shoot."

Driver Timothy Russell was shot 23 times. Passenger Malissa Williams was shot 24 times. No gun was found on them or in their vehicle. The chase had begun when an officer thought he heard a gunshot from a car speeding by the police and courts complex, jumped into his patrol car and radioed for help. Police don't know why Russell didn't stop.

Brelo fired a total of 49 shots. In all, 137 shots were fired at the schoolyard, authorities say. None of the other 12 officers who fired shots were indicted, McGinty said Friday. Five supervisors were charged with dereliction of duty for failing to control the chase.

The killings have been decried as a racially motivated execution – both victims were black – and are part of a wide-ranging federal investigation, including into the police department's use of deadly force and its pursuit policies.

The chase involved five dozen cruisers and wove through residential neighborhoods, onto Interstate 90 and eventually ended in east Cleveland. McGinty said the chase covered 20 miles over 23 minutes and reached speeds of 110mph.