He was arrested and loaded into the back of a police van, with his wrists and ankles shackled, but he was not strapped in with a safety belt. The van reportedly stopped six times during a rough 45-minute ride that caused him to be slammed about. Prosecutors say that during the van’s fourth stop, he suffered the critical injury that eventually killed him.
Porter was present during five of the six stops the police van made between the Gilmor Homes and the Western District police station, where Gray arrived unresponsive. He died in a hospital a week later.
Gray's death is one of several recent incidents in which black people who were unarmed or were not lethally armed died in police custody or were killed by police officers. Shortly after Gray's funeral in April, Baltimore was convulsed by riots and angry demonstrations.
During deliberations on Wednesday, a handful of protesters gathered outside the courthouse, chanting, "Send those killer cops to jail." After learning of the mistrial, protesters chanted, "No justice, no peace," and the demonstration spilled from the sidewalk and onto the street.
Mayor Stephanie Rawlings-Blake urged people to remain calm over the ruling. "We must respect the outcome of the judicial process," she said in a statement.
Officials in Baltimore came under heavy criticism for a restrained initial response to April's demonstrations, which some observers contended allowed arson and looting to spiral out of control.
"I urge everyone to remember that collectively, our reaction needs to be one of respect for our neighborhoods," Rawlings-Blake said. "In the case of any disturbance in the city, we are prepared to respond."
On Wednesday, scores of protesters marched through downtown Baltimore following the ruling, chanting "we have nothing to lose but our chains" and "the whole damn system is guilty as Hell."
Uniformed police officers took up positions throughout the city, including by the courthouse and police headquarters. Sheriff's office spokeswoman Maj. Sabrina Tapp-Harper said two people were arrested. Both are charged with disorderly conduct, failure to obey a law enforcement officer's command, and disturbing the peace by using a bullhorn outside the courthouse while court was in session.
Another group of protesters gathered in Gray's neighborhood, near where a drug store was burned during the rioting, where they expressed disappointment at the outcome.
"I think everyone in Baltimore wanted a conviction," said Westley West, the pastor of the Faith Empowered Ministries Church, who is black. "I feel it sends a bad message and gives the police hope that they will get away with brutality."
The Baltimore chapter of the NAACP echoed the mayor’s call for calm in a statement, asking for "frustration and anger to be controlled and the rights of all people respected, on all sides."
Local community group Baltimore Bloc and the national racial justice group Advancement Project released a joint statement on Wednesday that said the mistrial "delayed" justice. "Anything less than convicting Porter on all charges confirms that our criminal justice system does not value black lives," the groups said.
Rep. Elijah Cummings, D-Md., whose congressional district includes a large portion of Baltimore, issued a statement saying he was informed that State's Attorney Marilyn Mosby's office intends to retry Porter. A call to Mosby's office was not returned, as it had closed for the day.
Tessa Hill-Aston, president of the Baltimore branch of the NAACP, said that while a lot of people are upset that the trial ended in a mistrial, they recognize that they have a lot more to go through with five more trials of other officers charged in the case.
In closing arguments on Monday, prosecutors said Porter could have saved Gray's life with two clicks: one to buckle him in with a seat belt and another to summon medical help with his police radio. Defense lawyers said Porter was not to blame for Gray's death.
Porter took the stand in his own defense and testified that Gray showed no signs of pain or distress before he arrived at the police station critically injured.
Prosecutors said that was a lie. "Freddie Gray went into the van healthy, and he came out of the van dead," prosecutor Janice Bledsoe told jurors. The transport van "became his casket on wheels."
She showed jurors the unfastened seat belt from the transport wagon. "It's got Gray's blood on it," she said.
"Don't fall for that," countered Porter's attorney Joseph Murtha. He argued that expert witnesses disagreed on exactly when Gray's neck was broken during his trip to the police station and said this alone should give jurors reasonable doubt.
Gray's death was a "horrific tragedy," but "there is literally no evidence" Porter is responsible, Murtha said. "This case is based on rush to judgment and fear. What's an acronym for fear? False evidence appears real."
It wasn't clear how the mistrial would affect the state's cases against the other officers. Prosecutors planned to use Porter's testimony against two of his fellow officers.
Warren Brown, a Baltimore defense lawyer who was in the courtroom, said of the decision to declare a mistrial, "I am not surprised at all. I think you will have the same scenario with the other trials."
He said he wanted to see if the jury broke down on racial lines. Seven of the jurors are black, and five are white.
Another legal expert said he was surprised to see a mistrial declared on just the third day of deliberations.
"I thought the judge would never declare a mistrial, absent a fistfight, until the jury had been deliberating for six or seven days," said Jim Cohen, a professor at Fordham Law School in New York. "They chose the wrong defendant to try first."
Al Jazeera and wire services