DENVER -- Investigators returned to Coors Field Monday to try and determine why an escalator malfunctioned last week as fans were leaving a crowded baseball game.

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Escalator Victims: We Felt We Were Going To Die Family Describes Their Fall Down Escalator Hear From Eyewitnesses At Coors Field

The cause remains a mystery. Police said 35 people were injured when the crowded escalator increased speed without warning. Fortunately, none of the injuries were life-threatening.

City inspectors are trying to determine if the machinery malfunctioned or if there were too many people on the moving stairway. They expect to issue a report this week.

A man who worked in the industry for 45 years said the problem may have been a brake failure.

"One of those 26-plus safety devices caused the brake to be applied and the brake didn't hold and that's it," said escalator expert Carl White. "When the brake failed because of this load and the counterbalance load, it took off at a high rate of speed and that's what caused the acceleration they felt. And in every case it's always the same, where it's heavily loaded -- it's always the same, it accelerates."

A similar mishap occurred on an escalator at a mall in Albuquerque, N.M. The escalator brake failed and people tumbled to the bottom of the moving stairwell.

One woman told 7NEWS that a similar incident occurred while she and her granddaughter were riding an escalator at Coors Field earlier in the week.

Rockies officials have also admitted that another Coors Field escalator suddenly stopped after a May 24 game causing minor injuries to about a dozen fans.

All seven escalators at Coors Field will remain closed until an answer can be uncovered. The Colorado Rockies' next home game is Wednesday.

The Consumer Product Safety Commission conducted a study in 1994 and found there were approximately 33,000 escalators in the United States and about 7,300 accidents that resulted in hospitalization. That works out to about one accident per every five escalators a year.