The six Baltimore police officers who have been charged in the death of 25-year-old Freddie Gray turned themselves in on Friday afternoon. They have since posted bond.

"No one in our city is above the law," Baltimore Mayor Stephanie Rawlings-Blake said during a press conference earlier in the day.

The development comes after the Baltimore State's Attorney's office announced on Friday morning that Gray's death following his arrest by city police had been deemed a homicide, and that it had issued warrants for the arrest of six officers on various charges related to the murder.

State's Attorney Marilyn J. Mosby announced the decision at a news conference held Friday morning, declaring that police had no probable cause to justify Gray's arrest and that the officers involved were negligent in his death.

"We have probable cause to file criminal charges," she said, which include second-degree murder, manslaughter, assault in the second degree, misconduct in office, and false imprisonment.

The officers charged in Gray's death are Officer Garrett E. Miller, Sgt. Alicia D. White, Officer Caesar R. Goodson, Jr., Officer William G. Porter, Lt. Brian W. Rice, Officer Edward M. Nero.

Rice, Porter, Goodson, and White were all charged with involuntary manslaughter. Goodson, the driver of the police van that transported Gray after the arrest, has been charged with second-degree depraved-heart murder, which could land him 30 years in prison. The term "depraved heart" refers not to the victim's heart, but the perpetrator's. A depraved-heart murder is defined as a death that results from reckless and wantonly vicious behavior that the perpetrator realizes puts the victim in danger.

Gray sustained a severed spine and crushed voicebox in police custody after his arrest on April 12. His death a week later tapped into nationwide frustration over police abuse and discriminatory enforcement, inciting protests across the country as well as riots in Baltimore following his funeral earlier this week.

Friday's decision comes one day after police completed their investigation into the death, with the information used to inform the separate investigation carried out by city prosecutors.

"Gray suffered a critical neck injury during a police van transfer," Mosby announced. She said that he had requested medical care twice, but by the time he was taken out of the police transport vehicle and medical assistance was ordered, Gray was already severely injured, not breathing, and in a state of cardiac arrest.

Mosby called for calm and peaceful protest from demonstrators during the announcement.

"To those who are angry hurt or have their own experience of justice at the hands of police officers, I urge you to channel that energy peacefully as we prosecute this case," she said. "Your peace is sincerely needed as we seek justice on behalf of Freddie Gray."

She stressed that this was not an indictment of the entire Baltimore police force, highlighting her long family history in law enforcement, but pointedly admonished those in law enforcement with access to investigation details who have leaked information to the public.

"I strongly condemn anyone in law enforcement with access to trial evidence who has leaked information prior to the resolution of this case," she said. "You are only damaging our ability to conduct a fair and impartial process for all parties involved. I hope that as we move forward with this case everyone will respect due process and refrain from doing anything that will jeopardize our ability to seek justice."

Baltimore's police union put out a letter ahead of Mosby's announcement on Friday, saying that none of the six officers were responsible for Freddie Gray's death and insisting that they were diligent in the case.

"Not one of the officers involved in this tragic situation left home in the morning with the anticipation that someone with whom they interacted would not go home that night," the letter states. "As tragic as this situation is, none of the officers involved are responsible for the death of Mr. Gray."

The Fraternal Order of Police Lodge 3 (FOP), as the union is known, also asked the State's Attorney's Office to appoint a special independent prosecutor on the case, citing Mosby's ties to the lawyer representing the Gray family, William "Billy" Murphy, as well as to her husband, who is a city councilman.

"I have very deep concerns about the many conflicts of interest presented by your office conducting an investigation in this case," FOP President Gene Gyan wrote in the letter. "These conflicts include your personal and professional relations with Gray family attorney, William Murphy, and the lead prosecutor's connections with members of the local media."

The first comments from Gray's family emerged on Friday afternoon, with his mother, Gloria Darden, telling BuzzFeed she felt good about the State's Attorney's announcement.

"I feel good because we got all six of them" Darden told the media outlet shortly after Mosby's press conference. "You can rest, Freddie. You can rest. You can be in peace now."

In a televised statement on Friday, President Barack Obama said it was "absolutely vital" that the truth emerges in regards to what exactly happened to Freddie Gray. Obama called for continued peaceful protests, adding that he would work to rebuild trust between the community and police utilizing the so-called 21st Century task force the White House established at the end of 2014 in response to events in Ferguson, Cleveland, and Staten Island, that saw an unarmed black teenager, child, and man killed by cops on separate occasions.

"I'm actually gonna be talking to mayors who are interested in figuring out ways to rebuild trust between the community and police to focus on some of the issues that were raised by the task force right after this meeting," he said, noting that they would also be looking to improve opportunities for young people in these areas.

In a press conference on Friday following the State's Attorney's announcement, Democratic US Representative for Maryland's 7th District Elijah Cummings commented on the decision, calling it a historical moment in that often nothing happens as a result of these incidents. He said this was the beginning of a process.

"When I think about Freddie, I could not help but think about my own childhood," Cummings said. "I looked in that casket and said to myself 'here was a young man, just trying to exist' and so hopefully now with this our city can begin to heal and come together."