BALTIMORE — The first effort to convict an officer in Freddie Gray’s death from a broken neck in a Baltimore Police van ended Wednesday with a hung jury and a mistrial.

Officials appealed for calm as small crowds protested along streets lined with police officers. The situation was quiet at North and Pennsylvania, the intersection where the worst rioting happened in April as parts of West Baltimore were set on fire.

William Porter’s mistrial is a setback for prosecutors trying to respond to a citizenry frustrated by violent crime and allegations of police misconduct. Homicides have soared and the pressure on city officials has been unrelenting since Baltimore City State’s Attorney Marilyn Mosby charged six officers in Gray’s death.

About 30 protesters chanting “send those killer cops to jail” outside the courthouse switched gears after the mistrial was announced, chanting “No justice, no peace!” and “Black Lives Matter.”

The case hinged not on what Porter did, but what prosecutors said he didn’t do. He was accused of failing to get medical help for a critically wounded Gray and was charged with manslaughter, assault, misconduct in office and reckless endangerment, carrying maximum sentences totaling 25 years.

The judge planned to discuss a possible retrial with both sides in his chambers on Thursday.

Mayor Stephanie Rawlings Blake and the new police commissioner she installed after last April’s riots warned people against more violence.

“We will not, we cannot be defined by the unrest of the spring,” the mayor said.

“Protesters who are lawfully assembled have a friend in the Baltimore Police Department,” Commissioner Kevin Davis said. “Folks who choose to commit crimes and break things and hurt people are no longer protesters.”

Mosby wouldn’t comment: “Gag order,” she said, smiling and shaking her head inside the courthouse.