Police said they're looking for a man who fondled a woman on a Chicago Transit Authority Red Line train Wednesday morning.
According to a police-issued community alert, the assault happened on a crowded southbound train at about 8:30 a.m.
The offender, whose image was captured by surveillance cameras, was wanted for making "inappropriate contact" with a 23-year-old woman.
The suspect was described as a white male who stood between 5 feet, 10 inches and six feet tall. He had blonde or light brown hair and a light complexion, police said.
"I'm probably more cautious when I ride the Red Line than other lines for sure," a passenger told NBC 5.
"It sounds like it happens to often. A lot of hoodlums spoils the fun for the ride," another passenger said.
Police advised riders to always be aware of their surroundings, walk in pairs or groups, dial 911 to report suspicious activity and to never pursue a fleeing assailant.
The Guardian Angels said they plan to hand out pictures of the suspect from 5 a.m. to 10 a.m. Thursday at the Chicago station on the Red Line.