Protesters march Friday after the announcement of charges against the police officers involved in Freddie Gray's arrest in Baltimore. The stiffest charge, second-degree “depraved heart” murder, was filed against the driver of the police van that Gray was in after his arrest.

BALTIMORE — A massive march planned for Saturday to protest the death of a man in police custody is now being billed as a “victory rally” after Baltimore’s top prosecutor filed criminal charges against the six officers involved in the man’s arrest.

The thousands of marchers who are expected to hit the streets this weekend will now do so to celebrate the decision by State’s Attorney Marilyn Mosby to charge the officers with felonies ranging from assault to murder, and encourage continued peaceful demonstrations.

Freddie Gray’s death from spinal injuries a week after his April 12 arrest provoked riots on the streets of West Baltimore on Monday and quickly became a rallying cry against police brutality and social inequality in the city. Mosby’s announcement Friday triggered celebrations on those same streets.

Mosby said after reviewing the results of a police investigation turned over to her just one day before, she had concluded Gray’s arrest was illegal and unjustified. She said his neck was broken because he was handcuffed, shackled and placed head-first into a police van, where his pleas for medical attention were repeatedly ignored as he bounced around inside a small metal compartment in the vehicle.

The officers missed five opportunities to help the injured and falsely imprisoned detainee before he arrived at the police station no longer breathing, Mosby added. They even rerouted the van to pick up another passenger, she said.

The police had no reason to stop or chase after Gray, Mosby said. They falsely accused him of having an illegal switchblade when in fact it was a legal pocketknife, and failed to strap him down with a seat belt, a direct violation of department policy, she said.

Gray’s stepfather, Robert Shipley, said the family was happy the officers were charged, and he reiterated a plea to keep all public demonstrations peaceful.

“We are satisfied with today’s charges; they are an important step in getting justice for Freddie,” Shipley said. “But if you are not coming in peace, please don’t come at all.”

The family lawyer, Billy Murphy, said the charges are “a first step but not the last,” adding Baltimore now has an opportunity to set an example for cities across the nation grappling with police brutality.