Jerome Murdough, a mentally ill homeless man who was found dead in his jail cell last month on Rikers Island, likely died of dehydration or heat stroke and “basically baked to death” as his cell overheated, city officials said Wednesday to the Associated Press.

A medical examiner’s report on Murdough was inconclusive as to the mentally ill Marine veteran’s death, but officials told the AP that the 56-year-old most likely died from extreme dehydration or heat stroke. The New York State Department of Correction told the AP that there will be an investigation into Murdough’s death, “including issues of staff performance and the adequacy of procedures.”

Murdough’s case has riled advocates of mentally ill inmates who say the 56-year-old was mistreated by the criminal justice system. They claim Murdough should’ve been given mental health treatment instead of being arrested for trespassing when officers found him sleeping in the stairwell of a Harlem housing project in February. They also said Murdough’s $2,500 bail was excessive and that he wasn’t supervised closely enough.

"So Mr. Murdough violated the trespass law. So he suffered the consequences by going to jail," Jennifer J. Parish, a lawyer at the Urban Justice Center’s Mental Health Project, told the AP.. "But the jail system committed more serious harm to him. And the question is, 'Will they ever be held responsible?'"

Equipment in Murdough’s Rikers Island cell malfunctioned, causing temperatures to rise above 100 degrees. The inmate also didn’t open a small vent that would have let cool air into his cell.

“He basically baked to death,” one of the officials told the AP.

The mentally ill inmate’s mother, Alma Murdough, said she wasn’t notified about her son’s Feb. 15 death until the AP contacted her for its story. The DOC said Jerome Murdough’s attorney was told of his death three days after the 56-year-old was found dead in his cell.

Alma Murdough said her son suffered from bipolar disorder and schizophrenia. She last saw him three years ago.

"He was a very lovely, caring guy," she told the AP. "He had beer problems. Drinking beer. That was his downfall. Other than that, he was a very nice guy. He'd give you the shirt off his back."

Murdough was locked into his cell in the mental observation unit of Rikers around at 10:30 p.m. on Feb. 14, a week after he was arrested, according to the AP. Inmates in the unit are supposed to be checked every 15 minutes as part of a suicide watch, the officials told the news service. Murdough was found dead four hours later.

The mentally ill inmate was taking anti-psychotic and anti-seizure medications, which could have made him more vulnerable to the heat in his cell, Dr. Susi Vassallo of the New York University School of Medicine told the AP.  She said being in such heat for only a couple of hours could be fatal.

Wanda Mehala, a sister of Jerome Murdough, said the family is demanding answers.

"We want justice for what was done," she said. "He wasn't just some old homeless person on the street. He was loved. He had a life. He had a family. He had feelings."