Christopher Lopez, who was mentally ill, died at the San Carlos Correctional Facility in Pueblo, Colo., on March 17, 2013, while prison guards and medical personnel joked about him laying face down on his cell floor.

A video (below) shot by the Colorado Department of Corrections staff shows what happened to Lopez on his final day when he died of an easily preventable low blood-sodium level, reports 9 News.

Lopez, who was diagnosed with schizophrenia, was originally sentenced to two years in jail for trespassing (a misdemeanor) and then given another four years for allegedly assaulting a prison guard. He was sent to solitary confinement at the San Carlos Correctional Facility in May 2012, where he stayed for nine and a half months.

The U.S. is one of the few countries that uses solitary confinement on a regular basis.

The ACLU notes, "The mentally ill, disproportionately represented in solitary confinement, often become even more desperately ill, sometimes engaging in self-mutilation or even suicide."

On the day Lopez died, prison guards dressed in riot gear entered his cell because he didn't move towards the door.

Lopez was labeled a "non-compliant" inmate and placed in "special controls," which are for prisoners "that have become violent or destructive to themselves or others," according to the Colorado prison system's own guidelines.

Lopez was neither violent or destructive, but "was promptly placed in restraints and assisted into the transport chair," according to the lawsuit.

The video shows Lopez having what is called a "grand mal seizure" while wearing a prison hood and strapped to the transport chair for 34 minutes.

“He is taken unconscious from the restraint chair in his boxer shorts and left to die on the cold concrete floor of his holding cell still fully shackled while medical personnel and guards stand around and make idle chit-chat and do absolutely nothing to get him the medical attention he desperately needed,” Lopez family attorney David Lane told KDVR.

A nurse did enter Lopez's cell, failed to take his vital signs, but gave him two psychotropic medications, which are known to cause a low sodium level, which killed Lopez.

About 18 minutes after Lopez died, a mental-health clinician asks the dead man, "What are you doing? Why are you doing this? I can see you breathing."

Prison guards then joked with the clinician about how Lopez "liked" being on the floor.

CPR by paramedics would not begin until Lopez had been dead for over half an hour.

The Colorado Department of Corrections said in a statement that said in part: "In May of 2013, three of those employees were terminated. An additional five received corrective and/or disciplinary action."

However, no criminal charges were filed against any of the prison employees.

Sources: KDVR, 9 News, ACLU