BALTIMORE (AP) — Prosecutors on Wednesday dropped all remaining charges against the three Baltimore police officers who were still awaiting trial in Freddie Gray’s death, blaming police for a biased investigation that failed to produce a single conviction.

The decision means that no one will be held criminally responsible for the death of Gray, a 25- year-old black man whose neck was broken while he was unrestrained in the back of a police van in April 2015.

A judge had already acquitted three other officers, including the van driver who prosecutors considered the most responsible and another officer who was the highest ranking of the group. A mistrial was declared for a fourth officer when a jury deadlocked.

Gray’s death added fuel to the growing Black Lives Matter movement, set off massive protests in the city and led to the worst riots that Baltimore had seen in decades.

The case also led the police department to overhaul its use-of-force policy. All officers will soon be equipped with body-worn cameras, and the U.S. Justice Department has launched an investigation into allegations of widespread abuse and unlawful arrests by police. The results are expected soon. The officers also face an internal investigation.

Shortly after the announcement that charges would be dropped, a defiant State’s Attorney Marilyn Mosby held a news conference, saying there was “a reluctance” and “an obvious bias” among some officers investigating Gray’s death.

“We do not believe Freddie Gray killed himself,” she said, standing in the neighborhood where Gray was arrested, a mural of him on a wall over her shoulder. “We stand by the medical examiner’s determination that Freddie Gray’s death was a homicide.”

She walked up to the podium as people chanted “we’re with you,” and her remarks were punctuated by shouts of support.

Gray’s mother, Gloria Darden, stood by Mosby, saying police lied. “I know they lied, and they killed him,” she said.

Attorneys for the officers said justice had been served and praised police.