NEW YORK >> A malfunctioning damper diverted heat to the top level of a two-tier observation unit where a city official told The Associated Press a mentally ill, homeless veteran inmate “basically baked to death” in a cell that was at least 100 degrees last month, the head of New York City’s jails system told lawmakers Thursday.

Acting Department of Correction Commissioner Mark Cranston, testifying before the City Council’s committee on fire and criminal justice, said outside consultants found that a gauge on the lower level, which was calling for the heat, failed to register the high temperature on the upper level.

Fan belts on the roof of the Rikers Island unit where 56-year-old former Marine Jerome Murdough was found dead were also “faulty,” Cranston said.

“My condolences go out to the Murdough family,” he said. “I think it’s a terrible situation and I can’t imagine what they’re going through.”

Cranston testified at a previously scheduled budget hearing where lawmakers pressed DOC officials about rising overtime costs, increasing levels of violence and a growing mentally ill inmate population that now comprises about 40 percent of the roughly 12,000 inmates who make up the nation’s second-largest jail system.

Councilwoman Elizabeth Crowley, the committee’s chair, cited the AP’s report on Murdough’s death, detailing how he was arrested Feb. 7 on a misdemeanor trespassing charge for sleeping in an enclosed stairwell on the roof of a Harlem public housing building and was sent to Rikers Island after being unable to make $2,500 bail.

“I don’t believe he should have ever wound up on Rikers Island,” she said of Murdough, who was discovered dead in the early hours of Feb. 15. “I think our city did a great disservice to him and I think our city does this to hundreds of people if not thousands.”

The correction officer assigned to patrol the unit where Murdough was housed — who was supposed to check on the inmates every half hour after they were locked in their cells at night — was suspended for 20 days and could face further punishment after the investigation is completed, Cranston said. Murdough was left unchecked “no more than four hours,” he said.

Asked after the hearing why an observation aide — an inmate who is trained to patrol certain units to check on vulnerable inmates every 15 minutes — wasn’t assigned to the unit where Murdough was found, Cranston said he couldn’t comment. City rules require such aides to be assigned to certain units, including the mental observation unit.

A separate oversight hearing will be held next month to further question DOC officials about the Murdough case, as well as rates of violence, use-of-force incidents and the jailing of mentally ill inmates, Crowley said.

New York City’s jails are not the only one struggling with how to best treat an increasingly mentally ill inmate population. There are more than three times as many seriously mentally ill people in jails and prisons than there are in hospitals, according to a 2010 survey by the nonprofit Treatment Advocacy Center and National Sheriffs’ Association.

Mayor Bill de Blasio’s new correction commissioner, Joseph Ponte, begins next month. He has been touted as a reformer who reduced the use of solitary confinement in Maine, where he currently heads the state corrections system.

“Regarding the terrible tragedy of Mr. Murdough, you know, it’s almost a perfect storm of the city’s failed policies of homelessness, mental health, veterans’ services and corrections,” said City Councilman Rory Lancman, noting that Rikers Island has become the de facto institution where the city’s mentally ill end up.

Murdough, who was on anti-psychotic and anti-seizure medication, was found dead in the early hours of Feb. 15, four city officials told the AP. More tests are needed to determine exactly how he died, the medical examiner’s office said. But the officials, all with detailed knowledge of the case, said preliminary findings point to extreme dehydration.

Cranston confirmed Thursday that Murdough “would’ve had the ability” to open a small, vent-like window in his cell but didn’t.

Alma Murdough, 75, who said her son suffered from bipolar disorder and schizophrenia, wasn’t notified of her son’s death until nearly a month after it happened, when the AP contacted her.

On Thursday, Cranston told lawmakers the department’s notification process had been followed in Murdough’s case, but was being changed to more proactively find up-to-date contact information for relatives of incarcerated people.

“The reality of it is, if that procedure doesn’t result in notifying next of kin it has to be changed and it will be changed,” he said.

Murdough’s sister, Cheryl Warner, 44, said she wasn’t satisfied with the city’s punishment of the correction officer assigned to Murdough’s unit.

“Hopefully they get it right so it doesn’t happen to the next family,” she said of the proposed reforms to family notification.

Murdough was discharged as a private first class from the Marine Corps and served from 1975 to 1978 as a field artillery batteryman, the Marines Corps said. He struggled throughout his adult life with mental illness and alcoholism, according to his family.