Seven employees at a Taylorsville prison lost their jobs in an ongoing investigation into the death of a mentally ill inmate who had been held in solitary confinement.

N.C. Department of Public Safety spokeswoman Crystal Feldman said Wednesday that a captain and four nurses at Alexander Correctional Institution had been fired following the March 12 death of inmate Michael Anthony Kerr. A nurse and a staff psychologist resigned.

The 53-year-old Kerr was found unresponsive in the back of a van after being driven from Alexander to the mental hospital at Central Prison in Raleigh. The results of an autopsy are pending.

A police report on Kerr's death does not list any visible injuries and Walker said there was no indication of "foul play."

Kerr's sister, Brenda Liles, told The Associated Press last week she had repeatedly called prison officials in the days before her brother's death trying to get him help.

She said her brother had been struggling with mental issues since two of his sons were shot to death in separate incidents in recent years.

The prison system has asked the State Bureau of Investigation to review the circumstances under which Kerr died.

The department said Wednesday that it's conducting "an aggressive, yet thorough internal investigation."

"The department's goal is to complete the investigation swiftly, but most importantly it wants to find out what may have happened in this case," department spokeswoman Pam Walker said.

In a written statement issued last week, Public Safety Secretary Frank L. Perry expressed his condolences to Kerr's family and said administrators in the prison system had raised concerns about the death.

Records show Kerr, whose criminal record includes several 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.