(CNN) -- The death of a man being held in an Alabama jail last month has sparked a state investigation as well as a lawsuit from the man's family, claiming his body temperature was dangerously low after he received delayed medical attention and that he died of hypothermia.

The Alabama Law Enforcement Agency is investigating the death of 33-year-old Anthony Mitchell, who was transported from the Walker County Jail to a nearby hospital "for evaluation" and died on January 26, the agency said in a release. The investigation is at the request of the Walker County Sheriff's Office, the agency said.

In a federal lawsuit filed on Monday, Jon Goldfarb, an attorney for Mitchell's family, called his death "one of the most appalling cases of jail abuse the country has seen," and hailed a Walker County corrections officer for obtaining security camera footage within the jail. The corrections officer was later fired and a suit has been filed by Goldfarb on the officer's behalf for alleged retaliation.

Mitchell's family claims that a doctor saying Mitchell was hypothermic means he was likely "placed in a restraint chair in the jail kitchen's walk-in freezer or similar frigid environment and left there for hours," before his death, according to the lawsuit.

"The case provides contrasting examples of both the worst of humanity, and also its best. Without the malice, deliberate indifference, and failure to intervene of nearly a dozen correction officers at the jail, and the cooperation of these officers and their superiors in a scheme to deprive Tony of his civil rights and ultimately of his life, Tony could never have been killed," the suit said, adding "prompt emergency medical treatment" would have saved his life.

"But also, without the heroism of a corrections officer who dared to preserve security camera footage on her phone and get the recordings to the Estate, it would have been impossible for the Estate to dismantle the scheme of silence and lies within the Sheriff's Department and reconstruct what happened to Tony on the morning of January 26, 2023," the suit claims.

The medical examiner has not yet released Mitchell's autopsy report, the lawsuit states, which names Walker County Sheriff Nick Smith, several corrections officers, a nurse and an investigator as defendants.

CNN has reached out to Smith and the Walker County chief jail clerk for comment.

Death was 2 weeks after arrest

Mitchell was initially arrested by police on January 12, according to a Facebook post by the Walker County Sheriff's Office.

The office received a call from a concerned family member that Mitchell made statements insinuating that he may harm himself or others, the department said.

"When Deputies arrived, they observed Mitchell in the front yard of the residence. Mitchell immediately brandished a handgun, and fired at least one shot at Deputies before retreating into a wooded area behind his home," the post said.

After a search that involved the SWAT team, Mitchell was located inside a large metal structure in the woods and taken into custody where he was booked into the Walker County jail on charges of attempted murder. Deputies also found drugs and a handgun in the structure, the post added.

While he was incarcerated, the lawsuit claims officers on the overnight shift violated Mitchell's constitutional rights, with "deliberate indifference and malice," in intentionally exposing Mitchell to freezing temperatures.

A video clip obtained by the plaintiff's attorney from a guard at the jail purports to show two officers carrying Mitchell into the back of a sheriff's office vehicle. According to the lawsuit, this video shows Mitchell being transported on January 26 to the hospital. CNN is unable to independently verify the video.

"No medical personnel appear in this portion of the security camera footage," the suit says.

"This video clip captured events that took place at around 8:55 a.m. on January 26, 2023, after Tony had languished for five hours or more on a bare cement floor as his life trickled away, to the complete indifference of numerous corrections officers and medical staff," the suit continues.

"Tony's internal body temperature was 72 degrees Fahrenheit when he arrived at Walker Baptist Hospital in the back seat of a sheriff's vehicle on the morning of January 26, 2023, brought there by sheriff's deputies who did not even bother to call an ambulance for him despite his obvious need for emergency medical treatment," the lawsuit alleges.

The emergency room physician who treated Mitchell spent over three hours trying to resuscitate him, the lawsuit claims.

"I am not sure what circumstances the patient was held in incarceration but it is difficult to understand a rectal temperature of 72 degrees [Fahrenheit] 22 degrees centigrade while someone is incarcerated in jail," the lawsuit says, quoting the doctor's note. "The cause of his hypothermia is not clear. It is possible he had an underlying medical condition resulting in hypothermia. I do not know if he could have been exposed to a cold environment. I do believe that hypothermia was the ultimate cause of his death."

Corrections officer fired for retaliation, suit claims

In a separate lawsuit filed on Monday against Smith and two other employees of the sheriff's office, former Walker County Sheriff corrections officer Karen Kelly alleges she was fired for sharing video of the incident allegedly showing Mitchell inside the jail.

"Karen Kelly changed that narrative through her actions in this case. She publicized a video of the abuse leading to the death of an inmate named Anthony Mitchell so the horror of his death was not buried with him. When the Sheriff learned Kelly had exposed the crimes of his department, he retaliated and fired her," the suit alleges.

The lawsuit claims that Kelly was having "extreme emotional distress" over the situation and "needed someone outside of her department to see what had happened." According to the lawsuit, she shared the footage with a corrections officer at another law enforcement agency.

The video she shared then begin circulating on social media, the suit says.

The lawsuit alleges that her firing was an act of retaliation and that Kelly engaged in "constitutionally protected speech when she published the video that was a matter of public concern, including the revelation of the extreme abuse of an inmate."

"The evidence of abuse would have been buried with Tony Mitchell but for the bravery of a lone corrections officer who made a video of what really happened to Tony and shared one of them. And, they fired her for exposing the truth of this abuse," Goldfarb, who represents both the Mitchell family and Kelly in their lawsuits, said in a statement.

"There needs to be a federal statute requiring bystanders to report inmate abuse and providing statutory whistleblower protection to those who do. I sent a letter to the jail before we filed this case telling them to preserve all of their electronic recordings — if they have destroyed them then I can only imagine the horrors they have hidden," he continued.

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