Police laughed and joked as he lost consciousness in handcuffs. Minutes later, he died.

Warning: Distressing content.

He asked the police for help. They told him to stay on the ground, where he was handcuffed and writhing.

He said he was afraid the officers would kill him. They told him to relax. He asked for help again. They kept him pinned, his face in the grass, a knee on his back. He asked again.

Then Tony Timpa went unconscious. In less than 20 minutes he was dead.

The group of Dallas police officers detaining Timpa didn't seem to notice he was dying in front of them. They didn't check whether he was breathing, and they didn't look for a pulse. Instead, the officers laughed. They mocked the way he had squirmed around, clearly in distress - "like a roly poly," one said. They speculated about what sort of mental illness he might have, or what drugs he may have taken.

When Timpa stopped responding, the officers apparently assumed he was asleep. They kept laughing, making jokes about waking him up for school. They tapped him, shook him, but he didn't answer. "What happened?" one officer asked.

"I don't know, he just got quiet," another responded.

"Just, bloop," chimed in a third.

Timpa's last minutes alive were made public in a disturbing video obtained and published by the Dallas Morning News and NBC5, the result of a years-long legal battle for access to records related to the 32-year-old's death in police custody on Aug. 10, 2016.

The video, released Tuesday, challenged previous police claims that Timpa was aggressive and that they used only the force necessary to prevent him from rolling into a busy street. The footage also provides the clearest picture yet of that night three years ago, when Timpa called 911 asking for help.

The case has dogged the department and angered the city since the Morning News broke the story two years ago. Dallas police declined to comment on the newly released video.

"Because there is pending litigation surrounding this incident, we are unable to comment on the actions of the officers," department spokesman Carlos Almeida told The Washington Post.

That night, Timpa, an executive who drove a Mercedes, called authorities from the parking lot of a local porn store. He told a dispatcher that he was afraid. He had schizophrenia, he said, and he hadn't taken his medication. He was unarmed.

Growing up, one of Timpa's favorite books was "Peter Pat and the Policeman," his mother Vicki Timpa told the Morning News. From it, he learned: "If you're lost, ask a policeman for help," she said. So he did. And it was the last call he ever made.

Then Tony Timpa went unconscious. In less than 20 minutes he was dead.

A county autopsy report ruled that Timpa died "as a result of sudden cardiac death due to the toxic effects of cocaine and physiologic stress associated with physical restraint." The physicians who examined him ruled his death was a homicide.

"The stress of being restrained and extreme physical exertion contributed to his demise," they wrote.

The evidence unearthed by Vicki Timpa and her lawyers, along with the Morning News and NBC5, has led to an excessive force lawsuit in federal court and an indictment of three of the officers involved, Kevin Mansell, Danny Vasquez and Dustin Dillard. In March, the Dallas County district attorney dismissed the charges against them and they returned to active duty the next month.

By the time police arrived at the scene, two private security guards had already handcuffed Timpa.

"Hey, get on the ground," one of the officers said, sidling up to him.

As he squirmed, another officer told his colleagues to "just keep him down." He was restrained that way for more than 13 minutes, according to a Morning News analysis of the footage. As he's pinned down, an officer tells Timpa they're just trying to help. In the background, though, another officer can be heard noticing the upscale address on his ID and making a joke about a yacht club.

Officers then zip-tie Timpa's legs. With an officer still on top of him, Timpa's pleas fade to indecipherable grunts. He stops moving. "Tony, you still with us?" someone asks. Someone else asks if he's asleep. They all laugh.

The Ethical Society of Police, an association of police officers in St. Louis that advocates for change, criticized the officers' tactics in a Twitter post.

"They notice his breathing slowed, and joke about him being dead," the group wrote. "The indifference for the man is angering."

One officer claims he heard Timpa snore. Another compares him to a child who is refusing to wake up to go to school.

"Tony, time for school, wake up," one says as another guffaws.

"I don't want to go to school, Mom," an officer responds, mimicking a child. "Five more minutes, Mom."

After Timpa's limp body is lifted onto a gurney, Dillard asks, "Is he knocked out? Or, he ain't dead, is he? He didn't just die down there, did he?"

"I don't think he did," another officer responded.

"Is he breathing?" Dillard asked again.

As Timpa is wheeled away, Dillard says to the others, "Hope I didn't kill him."

They laugh.