Gray, 25, died after sustaining a neck injury while in police custody in April 2015. Three of the six officers charged in the case had already been acquitted.
"Justice has been done," said Gene Ryan, president of the Baltimore Fraternal Order of Police, said after the charges were dropped.
But the city's top prosecutor didn't quite see it that way. Baltimore State's Attorney Marilyn Mosby said the decision was "agonizing," and she slammed the way police handled their investigation into the case.
Mosby: 'Inherent bias ... when police police themselves'
More than a year ago, Mosby stood on her city's
courthouse steps and announced charges against the officers
. "No one is above the law," she said as she read out charges that ranged from second-degree depraved-heart murder to manslaughter to second-degree assault.
In a fiery address to reporters Wednesday, Mosby said she still believes Gray's death was a homicide. But now, she said, she realizes the criminal justice system needs "real, substantive reforms" to hold officers accountable.
"We could try this case 100 times, and cases just like it, and we would still end up with the same result."
Mosby said the case showed "an inherent bias that is a direct result of when police police themselves."
"There were individual police officers that were witnesses to the case, yet were part of the investigative team, interrogations that were conducted without asking the most poignant questions, lead detectives that were completely uncooperative and started a counter-investigation to disprove the state's case," she said, shouting into a microphone as she read her remarks.
Mosby, who comes from a long line of police officers, told reporters she isn't anti-police.
"I'm anti-police brutality. And I need not remind you that the only loss -- and the greatest loss -- in all of this was that of Freddie Gray's life," she said.
When Mosby first took on Gray's case, some praised how swiftly she acted
. Others, however, said there wasn't enough evidence
to convict the officers.
Gray's stepfather, Richard Shipley, said Wednesday that he supported Mosby.
"We are pissed about the decision of the trials and the outcome of all the trials that have happened here in the city. We are very proud of the prosecutors who handled the case and did their best to their ability," Shipley said. "We stand behind Marilyn and her prosecuting team and my family's proud to have them represent us."
Police union: Prosecutor's comments 'outrageous'
Standing at a podium with the six officers who were charged, the police union chief called Mosby's comments "outrageous and uncalled for and simply untrue."
Evidence, he said, showed there was no wrongdoing.
"The state attorney simply could not accept the evidence that was presented," Ryan said. "She had her own agenda."
Investigators concluded Gray's death was an accident, said Ivan Bates, an attorney representing one of the officers.
"The thing that bothers me is this: We always attack the criminal justice system. We have to let the criminal justice system speak for itself. It gets it right," he said.
Baltimore Mayor Stephanie Rawlings-Blake told CNN that the prosecution's decision to drop charges made sense, given how the judge had ruled in the trials of the other three officers.
"I think (Mosby) made a wise decision, because the judge has found in the past that the cases were thin," she said.
Police Commissioner Kevin Davis, who took over for former Commissioner Anthony Batts in October, said 30 "ethical, experienced, and talented" detectives worked on the case and a local newspaper reporter was given access to the investigation.
"We knew the community would need a transparent assessment from an independent third party," the commissioner said.
Davis said the decision to drop the remaining cases was a wise and thoughtful one. He also said the relationship with Mosby's office was inherently strong and will remain so.
The commissioner's office said the officers are on administrative duty until a review by the Montgomery County Police Department is finished.
Van ride was key part of investigation
Gray died a week after police stopped him on a Baltimore street.
During his arrest, officers placed Gray in the back of a police van, which made several stops.
By the time the van arrived at the police station, Gray was unresponsive.
His neck was broken and compressed, prosecutors said in court
, comparing the spinal injury to those suffered after a dive into a shallow pool.
What the officers faced
A pretrial hearing for Officer Garrett Miller had been set for Wednesday. Trials for Officers Alicia White and William Porter had been scheduled for the fall.
Baltimore Chief Deputy State's Attorney Michael Schatzow made the request to drop charges against them in court Wednesday.
Three officers were previously acquitted in the case: Edward Nero
, a bike officer involved in the initial police encounter with Gray; Caesar Goodson
, who drove the van that transported Gray; and Lt. Brian Rice
, the highest-ranking officer charged.
A retrial against Porter had been scheduled after a jury deadlocked
in the case against him in December.
The prosecution's announcement Wednesday closed the criminal cases against the officers. But they still face administrative reviews and possible discipline.
Ryan told reporters Wednesday that most of the officers are already back at work.