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CHICAGO (AP) _ Investigators worked Sunday to determine why scaffolding outside the John Hancock Center plunged more than 40 floors to the ground during a wind storm, killing three women in cars.

Broken glass still littered the streets around the 100-story Hancock building, the city's third-tallest building, which anchors the north end of the city's busy Michigan Avenue shopping district.

Still-dangling sections of broken scaffolding suspended by cables from the top of the building had been secured on Sunday as crews worked to board up dozens of windows shattered as the platforms blew against the glass.

The scaffolding platforms crashed to the ground Saturday as a storm whipped the area with wind that the National Weather Service said gusted to 60 mph.

The scaffolding was ``swaying around like a cat toy,'' said Jerome Manansala, who works at a deli inside the Hancock building.

Those killed by the falling debris were identified as Nanatta Cameron, 39, of Chicago; Melissa Cook, 29, of Chicago; and Jill Semplinski-Nelson, 27, of Olathe, Kan., the Cook County Medical Examiner's office said Sunday.

Cook and Semplinski-Nelson were cousins on their way downtown to go shopping before celebrating Cook's 30th birthday Saturday. Their mothers were in the car with them when the scaffolding fell.

Semplinski-Nelson's cousin, Melissa Rohrer, said her cousin had waved a pedestrian through the crosswalk just before the scaffolding fell.

``The chances of this happening are a kazillion to one,'' she said. ``If they had just gone through (the light) themselves, they would have been alive.''

City building officials said they wanted to know whether the two scaffolding systems, which had been left in place almost halfway up the building, was properly secured at the time of the accident.

A city ordinance requires scaffolding systems to be locked in position when not in use. City Building Commissioner Mary Richardson-Lowry said she did not know how or if the scaffolding was secured.

``All we know right now is where it ended up,'' Richardson-Lowry said.

The owner of the building, the Shorenstein Co., issued a statement saying it was ``shocked and saddened by the tragic accident'' and was working to secure the scaffolding.

The subcontractor operating the scaffolding for the maintenance project, Prime Scaffold of Bensonville, said it was investigating. No one answered the phone Sunday at Prime Scaffold.

Eight people were injured, including Semplinski-Nelson's mother, Betty Lou Semplinski, 56, who was in fair condition at Cook County Hospital Sunday with a broken leg and hip. Cook's mother, Linda Demo, was treated and released from Cook County.

A woman in her 50s was in critical condition Sunday at Northwestern Memorial Hospital, where four others had been treated and released, a hospital administrator said.

A 53-year-old man was treated for minor injuries and released from Grant Hospital on Saturday, officials said.