— The U.S. Attorney's office notified the state of North Carolina Thursday that it has opened a criminal investigation into the death of inmate Michael Anthony Kerr who was found unresponsive in the back of a van March 12. An autopsy determined that Kerr died of dehydration.

Kerr was held in solitary confinement for 35 days and cited twice for flooding his cell, according to prison records.

He was being transferred March 12 from Alexander Correctional Institution in Taylorsville to a mental hospital at Central Prison in Raleigh. An autopsy released in September says the 54-year-old inmate, who had schizophrenia, died of dehydration. The report also said he was receiving no treatment for the symptoms of his mental illness.

Public records released to The Associated Press show Kerr was placed in "administrative segregation" on Feb. 5. The status means an inmate is confined to a solitary cell for such reasons as "to preserve order where other methods of control have failed."

In the following weeks, records show Kerr was cited nine times by correctional officers for violating prison rules, including disobeying orders and "lock tampering." Inmates in the state prison system are often cited for lock tampering after repeatedly banging on the steel doors of their cells.

On Feb. 21 and again on Feb. 24, records show Kerr was cited for intentionally flooding his cell.

A written policy at the North Carolina Department of Public Safety allows prison staff to respond to the "misuse of plumbing facilities" by turning off the water to an inmate's sink and toilet.

"Whenever an inmate misuses the plumbing facilities in his or her cell, the officer in charge may order that the water to the cell be cut off," according to the prison policy and procedure manual. "The water may be cut off to prevent continuation of the misconduct or damage of the facilities or other property."

The following day, Feb. 25, records show Kerr was moved to "disciplinary segregation," another form of solitary confinement employed as punishment that inmates commonly refer to as being in "The Hole."

In Kerr's autopsy report, Dr. Susan E. Venuti of the North Carolina Medical Examiner's Office wrote that she was allowed to read an internal prison report into Kerr's death, though she was not permitted to make a copy. Venuti wrote that the report left unanswered key questions, including when the inmate last had food and water.

Because of the lack of information, the pathologist wrote that she was unable to make a determination about whether Kerr's death from dehydration should be classified as natural, accidental or homicide.

"The nature of the dehydration, whether as a result of fluids being withheld, or the decedent's refusal of fluids, or other possible factors, is unclear," Venuti wrote. "Since the circumstances surrounding the development of dehydration leading to the death in this incarcerated adult are uncertain, the manner of death is best classified as Undetermined."

For more than six months, North Carolina prison officials say they and agents from the State Bureau of Investigation have been working to get to the bottom of why Kerr died. There has been no indication of when, or if, the results of that probe will be publicly released.

Seven employees at Alexander have either been fired or resigned through the course of the investigation, including a guard captain, nurses and a staff psychologist.

The prison system also confirmed Friday that Dr. John Carbone, the prison system's chief of psychiatry, has been reassigned to a lower level position. The agency did not respond to questions about whether Carbone's demotion is related to Kerr's care.

Records show Kerr, whose criminal record includes convictions for larceny, was sentenced in 2011 to serve 31 years as a habitual felon after being charged with illegally possessing and discharging a firearm.

North Carolina's prison system has long faced scrutiny for its treatment of inmates with chronic mental illnesses. Numerous studies have shown that long-term isolation can have severe effects on the mental well-being of inmates, especially those already suffering from psychiatric disorders.

In 1997, a federal audit of Raleigh's Central Prison followed the death of inmate Glen Mabrey, a Vietnam veteran with mental illness who died from dehydration after being held in solitary confinement. Mabrey's water had been cut off for four days after he'd intentionally flooded his cell.