CHICAGO (CBS) — Three employees of a South Holland assisted living facility have been removed from their jobs, after an elderly woman died from an overdose of pain medication. Two other residents who were hospitalized the same day also have died, and understaffing might have been an issue.

The deaths of two other residents at Holland Home are under investigation. Six residents were hospitalized on the same day, Feb. 3, and three later died.

Dorothy Byrd, 98, died of morphine and hydrocodone toxicity, combined with hypertensive and atherosclerotic cardiovascular disorder, according to the Cook County Medical Examiner’s office. Her death has been ruled a homicide.

Two other Holland Home residents who were hospitalized the same day – 88-year-old Robert Rundin and 98-year-old Leon Krynicki – also have died, but authorities have not yet determined the causes of their deaths. Autopsies for those two men have not yet been completed, awaiting toxicological tests that could take weeks or months.

A police source said the facility apparently was understaffed following a snowstorm that buried the Chicago area in nearly two feet of snow.

Thomas Paris, an attorney for Byrd’s family, said one registered nurse and two certified nursing assistants were on duty the day Byrd and the other five residents were hospitalized. He said all have been removed from their jobs, and members of the South Suburban Major Crimes Task Force, and South Holland police, have met with prosecutors in connection to their investigation.

Paris said it’s his understanding the nurse used painkillers to sedate seven seniors at Holland Home. Six fell ill and were rushed to hospitals. Byrd died the next day. Rundin and Krynicki died about a month later. The other three residents who were hospitalized on February 3 have now recovered.

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.

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