New York City Mayor Bill de Blasio spoke out about the death of a mentally ill, homeless veteran who died last month in an overheated jail cell on Rikers Island, calling the tragedy "very troubling."

Experts say that Jerome Murdough, a 56-year-old former Marine, literally "baked to death" in a jail cell that reached at least 100 degrees on Feb. 15.

"We don't know all the facts yet ... but obviously the allegations we've heard so far are very troubling," said Mayor de Blasio on Thursday, according to the Associated Press. "My heart goes out to his family; we lost someone who served his country."

NYC officials said that Murdough was on anti-psychotic and anti-seizure medication, which may have contributed to why he died in the overheated cell. Although the cell had a small vent to let in cool air, Murdough reportedly did not open it. As a result, one of the officials, who remained anonymous, said Murdough "basically baked to death."

Early results from his autopsy and investigation point to extreme dehydration or heat stroke as the cause of premature death.

In response to the mayor's comments, Murdough's 75-year-old mother, Alma, said more had to be done to find out how her son died.

"They knew he had problems. There's no excuse," she said of her son, who she said had bipolar disorder and schizophrenia. "They've got a lot of stuff to check," she said of the investigation. "A lot of stuff to correct."

Murdough, who was discharged from the Marine Corps as a private first class after serving from 1975 to 1978, was initially arrested Feb. 7 on trespassing charges for sleeping in a public housing building in Harlem. He was sent to Rikers because he could not afford to post a $2,500 bail.

Advocates for mentally ill inmates say the city's justice system failed by arresting him instead of finding him help and by failing to supervise him properly in a special observation unit for inmates with mental illnesses.

The Grio notes that 40 percent of the 12,000 inmates in the nation's second-largest jail system are mentally ill, and a third of them suffer from serious mental problems.