The case against Baltimore Police Officer Edward Nero comes more than a year after the April 19, 2015, death of Gray became a symbol of the black community's distrust of police and triggered days of violent protests. Three of the officers charged are white, three are black.
A highlight of the trial could be the testimony of William Porter and Garrett Miller, two Baltimore officers who were also charged in connection with Gray's death. The state is compelling them to take the stand under immunity, meaning their testimony cannot be used to incriminate them at trial.
The decision on his guilt or innocence rests in the hands of Circuit Judge Barry Williams, who heard the prosecution Thursday accuse the officer of not following police protocol, arresting Gray without probable cause and failing to secure the shackled prisoner in the police van.
"The issue here is not one of danger, it's an issue of caring," Michael Schatzow, chief deputy state's attorney, told the court in opening statements. "Mr. Gray was put in a risky and dangerous position on the floor of that van."
Nero, who is charged with second-degree intentional assault, reckless endangerment and two counts of misconduct in office, was one of three bike officers involved in the initial police encounter with Gray on April 12, 2015.
Schatzow told the court Nero shackled Gray's legs and later, with the help of another officer, loaded the prisoner into the van.
"The defendant knew it was his duty to ensure the safety of Mr. Gray," the prosecutor said.
Marc Zayon, Nero's attorney, portrayed his client as a man devoted to public service, including stints as an EMT and volunteer firefighter. As a cop, Nero had no internal affairs complaints, according to Zayon.
The defense said the chase and arrests were legal. "Everything that was done in this chase was done correctly," Zayon said.
An officer's safety is essential when securing prisoners in the van, Zayon told the court. It was "impossible" for officers to seat belt Gray because the shackled prisoner was resisting.
"Officer safety is not an abstract thing for Officer Nero," Zayon said.
Capt. Martin Bartness, who formally oversaw police department directives, testified for the prosecution that a new seat belt policy for prisoners in vans went into place days before Gray's arrest. The change required officers to strap down prisoners in vans. He said the general orders were departmental policies, not laws.
"I think there are a number of practices that are subject to debate," Bartness said on cross examination, adding that officers "make discretionary judgments every day."
Another prosecution witness, Detective Edward Bailey of the inspections unit, said under cross examination that it's the responsibility of the van driver to restrain prisoners.
Prosecutors have said that Gray complained of having trouble breathing and asked for medical help as he was being transported in the van. He was unconscious when he arrived at a police substation. He died from spinal injuries in a hospital a week after his arrest.
Gray's death spawned protests that erupted on April 27, 2015 -- the day of his funeral -- into violent clashes with police and instances of looting and arson. Hundreds of people were arrested and more than 100 police officers were injured. City officials imposed a curfew, and the governor called in the National Guard to help restore order.