Baltimore prosecutors dropped the hammer Friday on six cops over the death of Freddie Gray, charging the officer who drove him in a police van with “depraved heart murder” and nailing five others for manslaughter and assault.

State’s Attorney Marilyn Mosby made the stunning announcement after receiving a report from the medical examiner that classified the 25-year-old Gray’s death on April 19 as a homicide.

“The findings of our comprehensive, thorough and independent investigation, coupled with the medical examiner’s determination that Mr. Gray’s death was a homicide, has led us to believe that we have probable cause to file criminal charges,” said Mosby, 35, who has been in office for just four months.

The unexpected announcement — officials had indicated it could take weeks before any decision on charges was made — set off a jubilant celebration on the same streets that had been rocked by a wave of arson, looting and violence just four days earlier.

Mosby methodically and passionately laid out the findings of her office’s investigation into what happened to Gray from the time he was arrested at 8:40 a.m. on April 12 after running away from cops to when he was rushed to a hospital in cardiac arrest about 45 minutes later.

She said that Gray was carrying a legal folding knife when caught — not an illegal switchblade, as cops had claimed — and that police had no probable cause to even place him under arrest.

“No crime had been committed by Mr. Gray,” Mosby said.

She said two bicycle cops — Baltimore Police Officers Edward Nero and Garret Miller — and Lt. Brian Rice wrestled Gray to the ground after a two-block chase.

The cops handcuffed him and placed him face down on the ground and summoned a police van to take him in for booking.

Once the van arrived, with Officer Caesar Goodson at the wheel, the three cops placed the cuffed Gray inside but did not secure him with a seat belt, she said.

The van drove off but stopped a few blocks later, and Rice, Nero and Miller took Gray out and put shackles on his legs, then returned him to the van face down, Mosby said.

“Once again, Mr. Gray was not secured by a seat belt in the wagon contrary to a BPD [Baltimore Police Department] general order,” she said.

Rice then ordered Goodson to take Gray to Central Booking.

Goodson, now the only cop in the van, stopped it again several blocks away to check on Gray but “at no point did he seek nor did he render any medical assistance for Mr. Gray,” Mosby said.

Goodson drove on but stopped yet again and called for another officer, William Porter, to help him check on Gray.

“Mr. Gray at that time requested help and indicated that he could not breathe. Officer Porter asked Mr. Gray if he needed a medic, at which time Mr. Gray indicated at least twice that he was in need of a medic,” she said.

But neither cop called for help, she added.

Porter was called away to back up cops at another arrest nearby, and “Officer Goodson, in a grossly negligent manner, chose to respond” to that incident, ignoring Gray’s pleas for help, Mosby said.

When he arrived to pick up the new prisoner, the two cops and Sgt. Alicia White checked on Gray — who was now unresponsive — but still did not call for medical assistance, Mosby said.

“Despite Mr. Gray’s seriously deteriorating medical condition, no medical assistance was rendered or summoned for Mr. Gray at that time by any officer,” Mosby said.

When the cops arrived at the Western District Police Station for booking, Gray was not breathing and was taken to a hospital with serious head and spinal injuries.

Police sources had told The Washington Post that the other prisoner in the van said Gray was trying to hurt himself.

But after the arrests were announced, that prisoner, Donta Allen, declared, “That man, for a fact, did not hurt himself,” The Baltimore Sun reported.

Sources said he suffered the neck injury in the wagon, possibly during a so-called “rough ride” — in which cops drive erratically so an unrestrained prisoner is bounced around.

“Mr. Gray suffered a severe and critical neck injury as a result of being handcuffed, shackled by his feet and unrestrained inside of the BPD wagon,” Mosby said — though she did not mention the “rough ride” allegation.

Goodson was charged with second-degree depraved-heart murder, manslaughter, assault and other charges. The depraved-heart charge alleges that a suspect demonstrated a depraved indifference to human life while acting in a manner likely to kill.

Rice, White and Porter were charged with manslaughter and assault. Nero and Miller face assault and false-imprisonment charges.

If convicted on all charges, Goodson would face up to 63 years behind bars. Rice would face up to 30 years, and Porter, Nero, Miller and White would face up to 20 years.

Mosby also said she had met with Gray’s family.

“I told them no one is above the law and I would pursue justice upon their behalf,” she said.

A police-union rep blasted the arrests as a rush to justice.

“As tragic as this situation is, none of the officers involved are responsible for the death of Mr. Gray,” Gene Ryan, president of Fraternal Order of Police Lodge 3, wrote in a letter to Mosby.

Mosby dismissed a call to appoint a special prosecutor in the case after the union accused her of being too close to the Gray family’s lawyer, Billy Murphy.

Murphy contributed $4,000 to Mosby’s campaign and served on her transition team.

Warren Brown, a Baltimore defense lawyer who supported Mosby’s opponent in the recent election that put her in office, said her handling of the Gray case was linked to her political ambitions and those of her husband, Baltimore Councilman Nick Mosby.

“She is a politician; her husband is a politician. This is a watershed event,” Brown said.

Ivan Bates, a former prosecutor and current defense attorney in Baltimore, said Mosby was under pressure to charge the cops.

“I think she has too much pressure to not indict, from the pressure of her husband’s constituents, of her mentor Billy Murphy, and of the pressure of making sure she wants to hold on to her job in four years,” Bates said.

Mosby said she has no bias against cops, noting she has police officers in her family.

“I come from five generations of law enforcement,” she said at Friday’s news conference. “My father was an officer. My mother was an officer. Several of my aunts and uncles. My recently departed and beloved grandfather was one of the founding members of the black police organization in Massachusetts.”

The six charged cops all arranged to turn themselves in and were taken to Baltimore Central Booking to be processed. Their bail was to be set by a court commissioner within 24 hours.

If they are not released or can’t make bail, they will go before a judge in District Court on Monday, a court spokesman said.

Additional reporting by Jamie Schram