Updated

Orville Lynn Majors, who was convicted of killing six people while he was a nurse at a rural Indiana hospital, has died while serving a 360-year sentence, state prison officials said Monday.

The 56-year-old Majors was having breathing problems and became unresponsive Sunday at the Indiana State Prison in Michigan City, according to the Indiana Department of Correction. He was taken to a nearby hospital, where he was pronounced dead.

Preliminary autopsy results show Majors had heart problems and died of natural causes, the department said.

Majors was convicted in 1999 on murder charges that he gave lethal injections of heart-stopping drugs to ailing patients in the mid-1990s at the former Vermillion County Hospital in Clinton, about 60 miles (96 kilometers) west of Indianapolis near the Indiana-Illinois state line. The jury couldn't reach a unanimous verdict on a seventh murder count.

He was suspected of causing dozens of more deaths.

Prosecutors said Majors injected the patients with epinephrine and potassium chloride while he was a licensed practical nurse in the four-bed intensive care unit of the rural community's hospital.

Prosecutors built their case around the fact that Majors was present, and often alone, when each patient died. They also presented as evidence vials of potassium chloride and syringes found by Indiana State Police investigators at a house where Majors once lived in.

Statistical studies linked Majors to as many as 130 of 147 deaths at the hospital's ICU — many involving sudden respiratory failures — from May 1993 to March 1995, but Judge Ernest Yelton didn't allow the information to be used as evidence at Majors' trial.

Yelton, who is now retired, said during the sentencing that Majors "was entrusted with these people's care. In response he committed diabolical acts that extinguished the frail lives of six people."

On Monday, Yelton said he realized many other families believed Majors killed their relatives and that the case leaves unresolved grief in the rural county of about 16,000 residents.

"It cut a broad swath across Vermillion County and caused an incredible amount of pain and anguish," he said.

Majors maintained his innocence and his defense attorneys presented medical experts and family doctors during his trial who said the seven patients he was charged with killing all died naturally.

Survivors of about 80 patients who died while Majors was at the hospital in Clinton filed wrongful-death lawsuits, said Terre Haute attorney Eric Frey, who represented many of the families. Most of those were settled through a state compensation fund for patients, he said.

Hospital administrators asked police to investigate in 1995 after another nurse's study found the ICU's death rate increased from 31 or less each year in the early 1990s to 120 in 1994. At least 15 bodies were exhumed over the next two years to test drug levels.

Frey said he believed it was clear Majors was responsible for many of the deaths, even though prosecutors narrowed their focus to only the cases they believed had the strongest evidence that Majors gave his patients unauthorized and lethal injections.

"These were not normal deaths," Frey said Monday. "At least one day the whole unit died — all four people in the unit died."

Yelton recalled that many relatives of patients who died attended Majors' trial even though he wasn't charged with killing their family members. Yelton said he knows many of those families wished they had certainty that Majors was involved in their loved ones' deaths.

"The fact that he was found guilty and the fact that he was going to spend the rest of his life in prison, I feel confident did give them some ease and some relief," Yelton said.

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This story has been corrected to show that Majors was pronounced dead at a hospital, not the prison.

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