CHICAGO (CBS) — An autopsy has determined one of three seniors who died after allegedly being given overdoses of painkillers at a South Holland nursing home succumbed to natural causes.

The Cook County Medical Examiner’s office said it has determined 98-year-old Leon Krynicki died primarily due to heart problems. His hospitalization on Feb. 3 might have been due to over-medication, but the medical examiner’s office said the medication did not contribute to his death about one month later.

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Krynicki and five other residents of Holland Home were hospitalized on the same day. Krynicki and two others – 98-year-old Dorothy Byrd and 88-year-old Robert Rundin – later died, while the other three have since recovered.

Byrd died the day after she was hospitalized. An autopsy determined she died of morphine and hydrocodone toxicity, combined with hypertensive and atherosclerotic cardiovascular disorder. Her death was ruled a homicide.

Autopsy results were still pending for Rundin, who died about a month later.

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Thomas Paris, an attorney for Byrd’s family, has said it’s his understanding each of the six patients who were hospitalized were given the same drugs.

Dorothy Byrd (Supplied photo)

Dorothy Byrd (Supplied photo)

According to Paris, Byrd was taking hydrocodone for back pain, but not at the levels found in her body when she died, and she was not prescribed any morphine, which also was found in her system in toxic levels.

Nursing home staffers are the focus of an investigation into allegations the patients were overdosed with painkillers, which a police source said might have been done to sedate them amid a staff shortage due to a snowstorm.

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Holland Home chief operating officer David Mills has said the facility is cooperating with police, and conducting its own internal investigation.