A homeless veteran, incarcerated for trespassing in a stairwell, has died in his cinderblock jail cell in New York’s Rikers Island where temperatures exceeded a hundred degrees because of a heating malfunction.

The Associated Press, which broke the story, quotes an unnamed official saying Jerome Murdough, 56, “basically baked to death.”

The city is investigating.

Murdough’s family members, proudly holding a portrait of him in his crisp Marine uniform, say he grew up in Queens, enlisted right out of high school and served a tour in Okinawa, Japan.

When he returned, they saw signs of mental illness and an increased appetite for alcohol.

He started wandering around the city, disappearing for months at a time. His mother told reporters he roamed in and out of halfway houses, hospitals and homeless shelters. And though she urged him to return to Queens and live at home, he refused, The New York Times reported.

News reports say he had built a criminal record: 11 misdemeanor convictions for trespassing, drinking in public and minor drug charges, said Ivan Vogel, a public defender who represented him at his arraignment on the trespassing charge.

On Feb. 7, with temperatures averaging 30 degrees outside, Murdough wandered into an enclosed stairwell on the roof of a New York City Housing Authority building in East Harlem, looking for a warm place to sleep. News reports say it was there he was found by police and arrested for trespassing.

“This is where I live, in the roof landing,” Murdough told police, The Times said, citing the criminal complaint.

News reports say Murdough’s bond was set at $2,500 — a price he could not afford. So he stayed in jail.

A week after the arrest — on Valentine’s Day — Murdough was taken into a 6-by-10 cinderblock cell at Rikers Island. He was in the mental observation unit, where he was supposed to be checked on every 15 minutes, officials told reporters. But he wasn’t, according to the AP.

Four hours later, at about 2:30 a.m. on Feb. 15, he was found dead.

The AP reported that the medical examiner’s office said an autopsy was inconclusive, but officials said initial indications point to extreme dehydration or heat stroke.

News reports say Murdough’s internal body temperature nearly matched the temperature in his cell: at least 100 degrees.

Officials said those temperatures could have been even higher before they found him slumped over in his bed in the cell, which, they said, had overheated because of malfunctioning equipment.

They said Murdough hadn’t cracked the small vent in his cell, as other inmates had done, to let in cool air. And they told the AP he had been taking anti-psychotic and anti-seizure medications, which could have made him more susceptible to the extreme heat in his cell.

His 75-year-old mother, Alma Murdough, told reporters she did not learn of her son’s death until last week when she was called by the AP.

In a statement issued Wednesday, Department of Corrections Acting Commissioner Mark Cranston said:

“The death of an inmate under our supervision is never acceptable. … The department is conducting a full investigation of the circumstances surrounding Mr. Murdough’s unfortunate death, including issues of staff performance and the adequacy of procedures.”