CHICAGO (CBS) — A 77-year-old Niles woman died Friday when two stone slabs fell on her at her home in north suburban Niles.

Mary Sullivan was at her home in the 6900 block of Jarvis Street when she fell down a stairwell, according to Niles police.

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As she fell, she pulled the stone slabs down on her while trying to keep herself from falling, Niles police said. The slabs were leaning against the stairwell.

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Sullivan was pronounced dead at 9:55 a.m. Friday, according to the Cook County medical examiner’s office. An autopsy on Saturday found she died of mechanical asphyxia and entrapment under the stone slabs. Her death was ruled an accident.

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