BALTIMORE — (CNN) When the jurors in the trial of William Porter went to bed Tuesday night, they were deadlocked over the fate of the Baltimore police officer charged in the death of Freddie Gray.

They’ll give it another go Wednesday morning.

Porter is the first of six police officers to be tried in Gray’s death from a neck injury sustained while in police custody, and its outcome could have a domino effect on the others.

The jury — made up of three black men, four black women, three white women and two white men — began deliberating Monday, 12 days after testimony began.

On Tuesday afternoon, they told the judge they’d been been unable to reach an unanimous decision.

If the trial ends with a hung jury, prosecutors would have the opportunity to try the case again.

“This would be a game changer,” CNN legal analyst Sunny Hostin said.

A hung jury may result in a decision to change the venue of the trial, she said, and could affect the cases of the other five officers who have yet to be tried. All six officers are being tried separately and consecutively.

Next up is the van driver, Caesar Goodson, whose trial is set to begin next month. Goodson, a black officer who is the lead defendant in the indictment, is charged with the most serious offense, that of second-degree murder with a depraved heart.

Authorities say Gray, a 25-year-old black man, broke his neck on April 12 while being transported in a police van, shackled but not wearing a seat belt. His death a week later sparked demonstrations and made him a symbol of the black community’s distrust of police.

Prosecutors say Porter, one of three black officers charged in the case, was summoned by the van’s driver to check on Gray during stops on the way to a police station. They say he should have called a medic for Gray sooner than one was eventually called and also should have ensured that Gray was wearing a seat belt.

Porter is charged with involuntary manslaughter, second-degree assault, reckless endangerment and misconduct in office.

For convictions on some or all of the first three charges, he would face no more than 10 years in prison combined. There is no statutory maximum sentence for the fourth charge, misconduct.

With a verdict possible this week, the city of Baltimore, which witnessed protests and unrest after Gray’s death, said it activated its emergency operations center Monday “out of an abundance of caution.”

Last week, Baltimore Mayor Stephanie Rawlings-Blake and Police Commissioner Kevin Davis cautioned the city to be respectful as the verdict gets closer.

“Whatever the jury decides, we must all respect the process,” the mayor said last week. “If some choose to demonstrate to express their opinion, that is their right, and we respect that right, and we will fight to protect it. But all of us today agree that the unrest from last spring is not acceptable.”

Davis sent a letter to the police force on Monday, saying, “Regardless of the outcome of this trial or any future trial, we refuse to surrender to the low expectations of those who wish to see us fail. … We serve because we know so many good and decent Baltimoreans need us to stand in between them and crime, disorder and chaos.”

Baltimore police canceled leave for officers who had days off from Monday through Friday. Officers will be scheduled to work 12-hour shifts instead of the usual 10 hours.

Prosecutors say Gray was arrested April 12 after two police officers on bike patrol made eye contact with him and he took off running.

Officers caught up to him, and they found a knife in his pants. Gray was arrested on a weapons charge, though prosecutors say the knife was a type allowed by Maryland law and police had no reason to detain him.

Porter was not involved until, authorities say, he arrived to look for a possible second suspect and help with crowd control while Gray was put into the van. Gray was unresponsive by the time the van arrived at a police station after making several stops in between.

Dr. Carol Allan, the assistant state medical examiner, testified last week that Gray probably received his neck injury before the fourth stop, most likely at some point when the van stopped suddenly.

But two physicians testifying for the defense said Gray’s injury likely happened after the fourth stop. The reason, they said, is that Gray would have been unable to speak at that stop had the injury happened earlier.

Porter conceded that Gray asked for medical help during stop four but said he did not call a medic because Gray didn’t appear to be injured and didn’t articulate what was wrong.

Porter testified he told the driver, Goodson, that Gray had asked to go to a hospital, and Porter emphasized in court that Gray was in Goodson’s custody.

During Monday’s closing arguments, prosecutor Janice Bledsoe argued that any officer in Porter’s situation would have called for medical assistance once Gray complained.

” ‘I need a medic.’ How long does that take?” the prosecutor asked. “How long does it take to click a seat belt and ask for a medic? Is two, three, maybe four seconds worth a life? That’s all it would have taken.”

Prosecutors also argued that Porter could have prevented the injury by ensuring Gray was wearing a seat belt while he was in the van.

But during his four-hour testimony last week, Porter said that of the roughly 150 prisoners he has placed in police wagons since joining the Baltimore Police Department in 2010, none was secured with a seat belt — in part, out of concern for officers’ safety while in the wagon’s tight quarters.

Prisoners were never secured with seat belts during field training, and though cadets were instructed to secure prisoners with seat belts, they were not shown how, Porter said.

During his closing arguments, defense attorney William Murtha said the prosecution’s case was full of holes.

“The state is asking you to insert facts into the blanks that don’t exist,” he told jurors.

Murtha told the jury that the law requires them to reach a verdict based on the “standard of a reasonable police officer.”

“There is an absolute absence of evidence that officer Porter acted in an unreasonable manner,” he said.

The-CNN-Wire ™ & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: CNN)