(Reuters) - The city of Baltimore was on Sunday to observe a day of prayer two weeks after a 25-year-old black man died of injuries suffered in police custody in a case that has led to criminal charges against six officers.

Freddie Gray's death last month was the latest in a string of police killings of unarmed black men that have sparked anger and protests across the United States over the past year. But in a sharp departure from many prior incidents, Baltimore prosecutors found the officers had broken the law both in arresting Gray and in roughly handling him.

"What happened in Baltimore sets the bar for prosecutors across the country," said State Senator Catherine Pugh. "It raises the standard of what you can do."

After a day of violence on Monday, when rioters torched buildings and cars and threw rocks at police, the mostly black city of 620,000 people has seen a week of largely peaceful demonstrations and marchers that swelled into the thousands of people on Friday and Saturday after charges were brought.

Maryland's Governor, Larry Hogan, called for a day of prayer and reconciliation on Sunday.

"As we begin to rebuild and restore, let us renew our faith in the true spirit of our city and its people," Hogan said. "I pray that tomorrow will be a day of reflection."

On Friday, prosecutor Marilyn Mosby said the Maryland state medical examiner had ruled Gray's death a homicide. She said he was unlawfully arrested and the officers repeatedly ignored his pleas for medical help while he was handcuffed, shackled and lying face down in the back of a police van.

Investigations of police killings of unarmed black men last year in Ferguson, Missouri, and New York had concluded the officers involved had acted within the law, triggering waves of sometimes violent protests.

Gene Ryan, president of the Baltimore Fraternal Order of Police, said he was disappointed with "the apparent rush to judgment" in charging the officers.

Police on Saturday arrested at least a dozen people for violating the 10 p.m. curfew that has been in place since Tuesday night. They were a tiny fraction of the thousands who marched through the city's streets for hours.

Officers in patrol uniforms, rather than riot gear, mingled with the crowd for much of the evening at an intersection where buildings had been burned in Monday's rioting. Police and citizens chatted amiably, in a possible sign of improving relations.

Travis Robertson, a 33-year-old law student, spoke to one officer.

"At first, I didn't want to listen to her because I have had bad experiences with police...," Robertson said. "But as we talked, I could see that she was one of the good ones. There are definitely bad officers out there, but there are good ones too."

(Reporting by Scott Malone; editing by John Stonestreet)