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.

The trial of William Porter was the first test of the city’s efforts to balance the frustration of Baltimore’s citizens with their need to rein in violent crime. Homicides soared after Baltimore City State’s Attorney Marilyn Mosby charged six officers in Gray’s death, and the pressure city officials has been unrelenting since then.

About 30 protesters gathered outside, chanting “send those killer cops to jail.” After the mistrial was announced, they chanted “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.

It was not immediately clear whether Porter will face another trial. He waived his right to appear at a hearing Thursday to discuss a possible retrial.

The mayor and police commissioner were to speak a news conference Wednesday evening, but Mosby wouldn’t comment. “Gag order,” Mosby said, smiling and shaking her head inside the courthouse.

Attorney Billy Murphy, who obtained a $6.4 million settlement for Gray’s family from the city before Porter’s trial, said he and Gray’s mother and stepfather also would speak, on the courthouse steps.

The jury of seven men and five women deliberated for about 15 hours over three days. On Tuesday, they indicated they were deadlocked, but Circuit Judge Barry Williams told them to keep at it, even as he denied their requests for help.

Jurors sent notes asking for an explanation of terms including “evil motive” and “bad faith,” the standards by which they were told to weigh the misconduct charge. The judge declined, and also denied requests for transcripts of trial testimony, leaving jurors to refer to their own recollections and notes.

“It is clear you will not come to a unanimous agreement on any of the four charges,” Williams said before dismissing the jurors. “You have clearly been diligent.”

At least two activists were arrested in the immediate aftermath of the mistrial. Kwame Rose, who was marched by sheriff’s deputies into the courthouse, had called the mistrial an “injustice.”

“We are going to fight for justice until it becomes a reality in our lives. A mistrial means that the prosecution did not do their jobs good enough,” he said.

Mayor Stephanie Rawlings-Blake repeated calls for Baltimore residents to respect the judicial process.

“If some choose to demonstrate peacefully to express their opinion, that is their constitutional right. I urge everyone to remember that collectively, our reaction needs to be one of respect for our neighborhoods, and for the residents and businesses of our city,” she said in a statement.

The Baltimore NAACP echoed that call, asking for “frustration and anger to be controlled and the rights of all people respected, on all sides.”

Erika Alston, a West Baltimore community leader who founded Kids Safe Zone after the April riots, said the mistrial leaves her “kind of numb,” even though she followed the trial and walked away feeling there was reasonable doubt that Porter committed manslaughter.

“It’s early. This is one of six. That’s mainly what I want the community to know and feel and hear … it’s not over,” Alston said. “I’m not expecting our community to repeat April, but it is a bit of a kick in the chest,” she added.

A local activist, Duane “Shorty” Davis, said, “the state’s attorney put on a weak case.”

“The prosecution had no intention of winning the case because of their relationship the police department. They’re not going to eat their own,” he said. “If any of the officers get convicted, it will be a surprise to me.”

After court adjourned, Porter conferred solemnly with defense attorney Joseph Murtha, then left, shielded by deputies from the media. Murtha declined to comment, citing a judicial gag order barring lawyers in the case from making public statements.

Gray was arrested while fleeing from officers and died April 19, a week after his neck was broken inside a police van as a seven-block trip to the station turned into a 45-minute journey around West Baltimore. The young black man had been left handcuffed, shackled and face-down on the floor of the metal compartment, and the autopsy concluded that he probably couldn’t brace himself whenever the van turned a corner or braked suddenly.

Porter is also black, as are two of the other five officers charged.

It wasn’t clear how the mistrial would affect the state’s cases against the other officers. Prosecutors had planned to use Porter’s testimony against two of his fellow officers.

Prosecutors argued that Porter was criminally negligent for ignoring his department’s policy requiring officers to seat belt prisoners, and for not calling an ambulance immediately after Gray indicated he needed medical help. Porter, who was driving a patrol car the day Gray was arrested, was present at five of the van’s six stops during its circuitous trip.

The defense said Porter went beyond the call of duty in helping the handcuffed and shackled prisoner move from the floor of the van to a bench in the wagon, and in telling the van driver and a supervisor that Gray said he needed to go to a hospital. The defense mainly cast blame on the van driver, Officer Caesar Goodson, whose trial is scheduled to begin Jan. 6.

Several other trials of officers charged in the deaths of black men also ended inconclusively this year.

In August, a North Carolina jury deadlocked in the trial of Randall Kerrick, a white officer in Charlotte-Mecklenburg charged with voluntary manslaughter in the September 2013 shooting death of Jonathan Ferrell, who was unarmed. Prosecutors said they won’t retry him.

In June, a South Carolina jury couldn’t reach a verdict in the retrial of former Eutawville Police Chief Richard Combs, who is white. His lawyer said Combs acted in self-defense in the May 2011 shooting of Bernard Bailey, who was unarmed. Combs pleaded guilty in September to misconduct in office and was sentenced to a year of home detention.

Contributors include Brian Witte in Baltimore and Randall Chase in Dover, Delaware.