Quinto, 30, lost consciousness while being restrained by Antioch police officers on his mother’s bedroom floor on Dec. 23, 2020. A doctor who contracts with the county Coroner’s Office has testified that the death was caused not by officers kneeling on Quinto’s back but by “excited delirium syndrome due to acute drug toxicity with disturbances” and “physical exertion.”

“Every time I look at the death certificate it makes me cry,” Quinto’s mother, Cassandra Quinto-Collins, said Wednesday afternoon, seated at a picnic table in the leafy backyard of her home. She grimaced as she recited the cause of death on the document: “Excited delirium.”

The diagnosis – roughly defined as sudden, aggressive and paranoid behavior leading to cardiac arrest – isn’t supported by the American Medical Association, which says it’s been used as “justification for excessive police force, disproportionately cited in cases where Black men die in law enforcement custody.” Physicians for Human Rights have said excited delirium, a term in use since the 1980s, “cannot be disentangled from its racist and unscientific origins.” BART in 2021 announced that its police would no longer use the “racist” term.

But it remains in use in Contra Costa County, where the Coroner’s Office cited excited delirium as the cause of death in a 2021 case also involving Antioch police restraining a man named Arturo Gomez Calel who was facedown.

Now Quinto’s mother is hopeful that new information could lead to a homicide ruling that seems to her like it’s based in reality. During a deposition, the county contract doctor acknowledged the possibility that Quinto died of asphyxiation from restraint, according to a court filing by attorneys for Quinto’s family.

The filing, filed Thursday and obtained by The Chronicle, argues that the autopsy conducted by county contractor Dr. Ikechi Ogan missed key signs that Quinto died of asphyxiation from the officers’ body weight.

The filing is intended to correct the record, Quinto family attorney Ben Nisenbaum said, though he wasn’t hopeful that the new information would lead Contra Costa District Attorney Diana Becton to reverse her finding that the officers hadn’t used excessive force. Nisenbaum said clearing the officers was not rational considering the evidence known even before the doctor’s new statements.

“We certainly hope that there is a change with respect to how the criminal justice system has dealt with this,” Nisenbaum told The Chronicle on Wednesday. “We think the officers should be charged.”

Quinto’s family had a private autopsy conducted by Dr. Bennet Omalu – the pathologist best known for his groundbreaking study of long term effects of concussion in the brains of football players – leading to the discovery of petechial hemorrhages in Quinto’s eyes. That’s a sign of asphyxiation. During a deposition, Ogan was shown a photo of Quinto’s eyes taken in the private autopsy. He agreed that the pictures showed “quite large and very prominent” hemorrhages, said the Quinto family court filing.

“Dr. Ogan then testified,” the filing said, “that the presence of the petechia documented by Dr. Omalu had caused him to have a new opinion as to Mr. Quinto’s cause of death: the disruption of Mr. Quinto’s respiration was a factor in Mr. Quinto’s death.”

The Sheriff-Coroner’s Office didn’t immediately respond to a request for comment. The District Attorney’s Office had no immediate response.

In Ogan’s autopsy report, he had downplayed the possibility that weight on Quinto’s back played a role in his death, the court motion said, and he didn’t bring it up at all during a coroner’s inquest. He said Quinto had tested positive for a stimulant often used for narcolepsy, though Quinto’s family said they believe he took it, like many fellow gamers, to stay up playing video games. Ogan also noted the presence of a medication used to treat seizures, which Quinto’s family said they believe he was given when he arrived at the hospital.

In Contra Costa County, Sheriff-Coroner David Livingston holds coroner’s inquests asking juries to determine whether deaths involving law enforcement are due to one of four causes: accident, suicide, natural causes or the actions of another person — more commonly known as homicide. It’s a procedure most jurisdictions abandoned long ago and one that gets a lot of criticism as an unfair process where key witnesses – such as Quinto’s mother – may not get to testify.

After hearing from the county’s doctor, the jury ruled the death an accident. The juries’ findings aren’t binding, meaning prosecutors don’t have to accept them.

Quinto’s sister Bella Collins, 20, told The Chronicle that she called 911 two nights before Christmas 2020 because her brother was behaving strangely and was afraid he was going to die. Quinto, whose family said his confounding episodes had started suddenly that year, had been trying to pull his mother and sister close, begging them not to leave. The sister and mother insist he didn’t attack them, only held onto them for comfort.

Antioch officers – who at the time didn’t have body cameras – arrived, cuffed Quinto and restrained him on the floor of his mother’s bedroom. The mother said she watched as one officer at a time held Quinto down with a knee to his back and shoulder. She started recording a video with her cell phone.

“I stayed in the bedroom,” Quinto-Collins recalled. “I was really watching him.”

In cell phone audio and video viewed by The Chronicle, Quinto is facedown, saying nothing. His mother wonders if he’s asleep. No one is raising their voice. Then officers turn over her son, and she sees his face has turned purple and is bleeding.

Quinto-Collins’ video was part of the evidence reviewed by the District Attorney’s Office.

“While there are conflicting medical opinions as to the cause of death,” the report clearing the police said, “the accounts of what transpired in the bedroom are consistent among all witnesses.”

Quinto’s mom said that’s simply not true. She also took issue with the report’s mention that Quinto had fentanyl in his system. That drug, too, was given to him at the hospital, the family said.

Ever since Quinto’s death, the family said they’ve felt the force of Contra Costa County’s criminal justice system trying to excuse the officers at every turn and ignoring their concerns. Meanwhile, they’ve become fixtures at demonstrations over other deaths in police custody and lobbied for changes to state law, including to separate the sheriff and coroner’s office to increase checks and balances.

All but 10 of California’s 58 counties have combined sheriff’s and coroner’s offices.

“We said since the beginning, there were two crimes committed that night,” said Quinto’s stepfather Robert Collins. “One was the excessive force that killed Angelo. The second crime was the subsequent cover up that began that night.

“The other victim is the truth,” Collins added.

Reach Joshua Sharpe: joshua.sharpe@sfchronicle.com