The incident occurred August 28, 2012, around 4:20 p.m., inside the Daley Building at 14 East Jackson Boulevard, said officials.
Citing the official police report, the victim was on an elevator with 15 to 20 other people.
When most of the people got off, an unknown male offender, who was also on the elevator at time, shoved the victim into a corner.
When an eyewitness saw what was happening, the Good Samaritan pushed the offender and the victim was able to escape, said police.
After the strong arm robbery, the mugger stayed on the elevator and may have gotten off on one of the upper floors of the building.
The thief stole the victim's pink I-Phone, said police.
NOTE: The suspect's demographics, which includes his race, was removed from the police report.