NEW YORK (AP) — The mother of a mentally ill, homeless veteran who was found dead in a 100-degree Fahrenheit (38-Celsius) New York City jail cell that overheated due to an equipment malfunction said she is angry at city officials and plans to file a $25 million wrongful death lawsuit against the city.

"I know he was yelling for help and nobody ever came," Alma Murdough, 75, said at a news conference, surrounded by family. "He was hollering for help, and nobody came."

Her attorney, Derek Sells, said he has filed court papers to demand the city preserve all communication related to the death of Jerome Murdough.

Sells said Murdough, a 56-year-old former Marine, should have had around-the-clock supervision while jailed at Rikers Island following a misdemeanor trespassing arrest.

The Associated Press first reported in March on suspicions about Murdough's cause of death in February. One official who spoke at the time on the condition of anonymity described him as having "basically baked to death."

Sells last month filed a notice of claim, the first procedural step necessary for a civil suit against the city, with the comptroller's office. In it, he writes that Murdough's death was caused by carelessness and negligence by employees of the Department of Correction, or DOC.

Prosecutors are investigating the death.

"This case involves a tragic incident and we will review the lawsuit and respond accordingly," said Nick Paolucci, a spokesman for the city's law department.

Corrections officials have declined to comment, citing the ongoing criminal investigation.

Citing a preliminary DOC investigation, court documents filed last month in a separate federal court case show that Murdough's internal body temperature, taken nearly four hours after he was discovered unresponsive in his cell, was 103 degrees Fahrenheit. (40 Celsius). Murdough was slumped at the edge of the foot of his bed with "a pool of vomit and blood on the floor," the documents said.

A spokeswoman for the medical examiner's office says the exact cause and manner of Murdough's death have not yet been determined, pending further studies. But the court documents show the medical examiner investigator assigned to Murdough's case preliminarily found he likely died of hyperthermia.

Murdough was on psychotropic medication at the time of his death, which experts say can make people sensitive to heat. DOC officials have said he was left unattended for hours.

Murdough was arrested Feb. 7 on a misdemeanor trespassing charge for sleeping in an enclosed stairwell on the roof of a public housing building and was sent to Rikers Island after being unable to make $2,500 bail, according to court records.