BALTIMORE (AP) — No video captured what happened to Freddie Gray inside the police van where officers heaved him into a metal compartment after pinning him to a sidewalk. The cause of his fatal spine injury has not been revealed.

But a troubling detail emerged as hundreds of protesters converged on City Hall again Thursday: He was not only handcuffed and put in leg irons, but left without a seat belt during his trip to the station.

Unbelted detainees have been paralyzed and even killed by rough rides in police vans.” It even has a name: “nickel rides,” referring to cheap amusement park thrills.

Police brutality against prisoners being transported was addressed just six months ago in a plan released by Baltimore officials to reduce this misconduct. Department rules updated nine days before Gray’s arrest clearly state that all detainees shall be strapped in by seat belts or “other authorized restraining devices” for their own safety after being arrested.

Gray was not belted in, said attorney Michael Davey, who represents at least one of the officers under investigation.

But he took issue with the rules.

“Policy is policy, practice is something else,” particularly if a prisoner is combative, Davey told The Associated Press. “It is not always possible or safe for officers to enter the rear of those transport vans that are very small, and this one was very small.”

Commissioner Anthony Batts said there are no circumstances under which a prisoner should not be wearing a seatbelt during transport.

“He wasn’t wearing a seatbelt and that’s part of our investigation,” Batts told The Associated Press on Thursday. “It’s our responsibility to make sure people are safely transported, especially if their hands are behind their back.”

Batts also said another man who was in the van during the tail end of Gray’s ride told investigators that Gray was “was still moving around, that he was kicking and making noises” up until the van arrived at the station.

But Batts was careful to say that the investigation includes “everything the officers did that day.”

The Gray family’s lawyer, Billy Murphy, said “his spine was 80 percent severed” while in custody. It’s not clear whether he was injured by officers in the street or while being carried alone in the van’s compartment.

But if it happened on the way to the station, it wouldn’t be the first such injury in Baltimore: Dondi Johnson died of a fractured spine in 2005 after he was arrested for urinating in public and transported without a seat belt, with his hands cuffed behind his back.

“We argued they gave him what we call a ‘rough ride,'” at high speed with hard cornering, said Attorney Kerry D. Staton. “He was thrown from one seat into the opposite wall, and that’s how he broke his neck.”

Staton obtained a $7.4 million judgment for the family, later reduced to the legal cap of $200,000.

It also has happened in Philadelphia, where police in 2001 barred transportation of prisoners without padding or belts after The Philadelphia Inquirer reported that the city had paid $2.3 million to settle lawsuits over intentionally rough rides, which permanently paralyzed two people.

Gray fled on foot and was captured on April 12 after an officer “made eye contact” with him outside a public housing complex, police said. Videos show Gray screaming on the ground before being dragged, his legs limp, into a van. Witnesses said he was crying out in pain.

Kevin Moore, a friend of Freddie Gray’s who recorded video of his arrest, told The Baltimore Sun that police had Gray’s legs bent “like he was a crab or a piece of origami.”

Police procedures require officers to get immediate medical help if detainees need it, and to avoid aggravating any injury.

In Gray’s case, he repeatedly asked for help during the trip, but the driver instead diverted to another location to pick up another prisoner.

For the first time, the fire department released a timeline for paramedics’ response. Gray was arrested at 8:42 a.m. Paramedics received a call for an unconscious male at 9:26 a.m., Baltimore City Fire Department spokesman Captain Roman Clark said.

Medics arrived at the police station at 9:33 a.m., but didn’t leave for the hospital until 9:54, arriving roughly an hour and 20 minutes after his arrest. Clark didn’t say why it took more than 20 minutes to leave for the hospital once paramedics arrived.

“How did his injuries occur?” said Robert Stewart, a former chief who consults with police and the Justice Department on use of force. “These guys are picking up someone who is obviously injured.”

The driver also has a responsibility to refuse to take a seriously injured prisoner to the station if he belongs in a hospital, Stewart said.

“If I’m the officer in the wagon, if the guy’s hurt, I’m not taking him,” he explained.

All six officers involved in Gray’s arrest have been suspended with pay while under criminal investigation. Davey, whose firm is on contract with the Baltimore Fraternal Order of Police Lodge 3, said five of the six officers gave voluntary statements the day of Gray’s arrest, and one — he didn’t say who — declined to speak with investigators.

It’s quite common for prisoners to yell and complain, saying they’ve been injured or feel sick or that their handcuffs are too tight.

“You have to make a judgment call: is this a tactic, something to distract me?” said Lt. Luis Fuste of the Miami-Dade Police Department. “You’re taught that these things are often done with an ulterior motive.”

Yet Fuste and other law enforcement experts say rough rides aren’t typical, and aren’t worth the trouble to officers.

“Once he is a prisoner he is absolutely your responsibility,” said Peter Moskos, a former Baltimore officer who teaches law and police science at John Jay College of Criminal Justice in New York. “Even if there was no malign intent, even if there was no assault, he’s your prisoner. He goes into the wagon alive, he can’t come out dead.”

The Department of Justice is investigating whether Gray’s civil rights were violated, and an internal police investigation will be delivered by May 1 to the state’s attorney’s office, which will consider filing any criminal charges.

But some details have already been made public as authorities try to restore trust with a community demanding transparency and justice.

Commissioner Anthony Batts said Monday that officers repeatedly ignored Gray’s requests for medical attention before he was hospitalized in critical condition. “He asked for an inhaler, and at one or two of the stops it was noticed that he was having trouble breathing,” Batts said. “We probably should have asked for paramedics.”

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Associated Press Writers Dave Dishneau and Jeff Horwitz contributed to this story from Baltimore. Anderson reported from Miami. They can be reached at http://twitter.com/Miamicurt, http://twitter.com/ddishneau and http://twitter.com/JulietLinderman