BALTIMORE— Fourteen months after the death of a black man whose neck was broken in a police van prompted massive protests, spawned rioting and toppled the careers of Baltimore’s police commissioner and a Democratic mayor poised for re-election, authorities abandoned efforts to punish the officers involved.

The city’s top prosecutor was righteous in her rage Wednesday as she made official what was already clear after four failed attempts to prosecute: no one will go to jail for Freddie Gray’s death.

Earlier in the day, Baltimore State’s Attorney Marilyn Mosby had dropped the cases against the rest of the six police officers charged in Gray’s death after prosecutors had suffered blow after crippling blow as a judge acquitted three others in rapid succession. Instead of conceding defeat, she blasted the police department for a biased investigation she blamed for failing to secure a single conviction.

“The prosecution of on-duty police officers in this country is surprisingly rare and blatantly wrought with systemic and inherent complications,” the Democratic prosecutor said. “Unlike other cases where prosecutors work closely with the police to investigate what actually occurred, what we realized very early on in this case was that, police investigating police — whether they’re friends or colleagues — was problematic. There was a reluctance and bias that was consistently exemplified.”

Gray died a week after he suffered a spinal injury in the back of the detainee wagon while he was handcuffed and shackled, but not buckled in with a seat belt. Prosecutors alleged the officers involved in his arrest and transport were criminally negligent when they failed to use the seat belt, instead placing Gray face-down and head-first on the floor of a prisoner compartment. The state also said the officers erred when they chose not to call a medic after Gray indicated he wanted to go to a hospital.

Last May, Mosby said in announcing the charges that her decision to prosecute was based on both a police department investigation and a separate, independent investigation conducted by her office.

Three of the four officers who stood trial elected to have Circuit Judge Barry Williams hear their cases without juries. Williams then ruled three times in a row that although the officers may have exercised poor judgment, the state presented no evidence to prove they meant to hurt Gray.