CHICAGO (CBS)– Just days after 15 people were rescued from an elevator, the city’s investigation continues and it appears the weight on board exceeded capacity.

For an elevator to be ADA compliant, it has to be able to handle about 2,500 pounds.

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During the emergency evacuation Sunday morning, 10 people exited through an escape hatch in the roof and the other five people reportedly could exit only after crews cut a hole in the sheetrock of the elevator shaft.

The incident took place at a building located in the Loop at 819 S. State St.

“Fifteen people in an elevator might be the reason it got stuck,” Richard Gregory of Vertex Corporation said.

As an elevator engineering expert, Gregory’s thoughts are echoed by the city. City inspectors report the elevator began to fall and it’s emergency systems kicked in.

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Complicating the situation, the elevator came to a stop in the garage areas between the first and fourth floors without any doors, an area known as a blind hoistway.

“For an apartment building of this height, it’s unusual to have a blind hoistway at all,” Gregory said.

Fire crews are trained to get people to safety as soon as possible, and Gregory believes that’s most likely why they cut through a wall for the evacuation, instead of waiting for engineers to arrive on scene.

“I am 99.9 percent certain the elevator company could have moved the elevator within 6 inches of a door,” Gregory said.

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This incident is still under investigation and two units servicing the 9-story structure’s lower floor garage were marked out of service by the city.