Relatives of a man whom investigators determined died after a Kansas sheriff’s deputy shoved his knee into the cuffed man’s back for a minute and 26 seconds have filed a federal lawsuit.

Attorneys for the family of Charles Adair renewed their demand on Friday that video of what happened be released publicly in announcing the wrongful death lawsuit.

Filed earlier in April, the lawsuit names the Wyandotte county sheriff, the unified government for the county and Kansas City, Kansas, and Richard Fatherley, who was charged in September with second-degree murder in Adair’s death.

“The public has a right to transparency when someone dies in custody in this manner,” civil rights attorney Ben Crump, who is representing the family, said in a news release.

Crump and another civil rights attorney, Harry Daniels, were allowed to view video of what happened. The sheriff’s office has declined a records request from the Associated Press seeking the video.

Adair was arrested in July on misdemeanor warrants for failure to appear on multiple traffic violations. At the time, Adair’s leg needed to be amputated and was so badly infected that he was taken straight to the hospital, a Kansas bureau of investigation agent wrote in the affidavit.

Before Adair was cleared to return to the jail, he was diagnosed with a type of bone infection that sometimes develops in people with diabetes. A medical screening also found he was schizophrenic, the affidavit said.

The lawsuit said he was incoherent and that deputies believed Adair’s medical condition “was affecting his brain”.

After having his leg rewrapped the following evening, he got into an argument with the deputy who was wheeling him back his cell. Adair ultimately threw himself out of the wheelchair, the affidavit said.

Once he was back in his cell, he was placed on his stomach on the bottom bunk, with his legs and knees on the ground. The lawsuit and court records said he repeatedly yelled: “Help!”

The lawsuit said Adair was complying with commands but that Fatherley “pressed his body weight on to Mr Adair’s back”. Other deputies then removed Adair’s handcuffs while Fatherley shifted his weight forward.

The lawsuit said none of the other officers who were present intervened and that the deputies failed to modify their tactics to account for Adair’s apparent mental health impairment.

The lawsuit also said Fatherley, who is on administrative leave and free on bond, was not cut off from his sheriff’s office email after he was charged, allowing him to communicate with other members of the agency and employees that he knew were witnesses.

Wyandotte county sheriff’s captain Michael Kroening said Fatherley’s email was deactivated on 13 April after the litigation was filed. He declined to comment further because the litigation is pending. A county spokesperson didn’t immediately return an email seeking comment.

A status conference in the criminal case against Fatherley is set for May. His attorney, James Spies, has said that Adair’s death was “a tragic accident” but it was not a result of Fatherley’s actions. A phone message left at Spies’s law firm was not immediately returned.