The six officers face charges that, if they are convicted, could lead to decades in prison, based on their alleged actions that day. Among them: Illegal arrest, misconduct, assault and involuntary manslaughter.
Officer Caesar R. Goodson Jr., who prosecutors say was driving the van used to transport Gray after his arrest, faces the most charges, and the most severe: second-degree depraved heart murder.
"As our investigation has continued, additional information has been discovered, and as is often the case during an ongoing investigation, charges can and should be revised based upon the evidence," she said.
Mosby didn't take questions at the press conference and didn't go into details about what additional evidence had come to light.
The officers are scheduled to be arraigned on July 2, she said.
Attorneys for the officers have called for Mosby to be taken off the case, arguing that she has conflicts of interest -- an accusation Mosby denies.
In a statement after the officers' indictments, the police union called for the community to support police, noting that thousands of men and women in the department protect and serve the city's neighborhoods
"All citizens are innocent until proven guilty, including these six officers," Baltimore City Fraternal Order of Police President Gene Ryan said.
A lawyer representing Sgt. Alicia White, who faces charges of involuntary manslaughter, assault, misconduct and reckless endangerment, denied the accusations.
"I look forward to trying this case against Marilyn Mosby herself and proving Alicia White is innocent," attorney Ivan Bates said.