CHICAGO (CBS) — Police were warning women who ride the CTA about a man who has been snatching necklaces off women’s necks, then running off the train as the doors are closing.

Area Central detectives issued a community alert, warning people to be on their guard in the University Village, South Loop, and Noble Square neighborhoods, and their surrounding areas.

Police cited at least three robberies on Blue Line and Red Line trains – the first on July 27, on a Blue Line train near at the UIC-Halsted stop; the second on Aug. 3, on a Red Line train at the Cermak-Chinatown stop; and the third on Aug. 12, on a Blue Line train at the Division-Milwaukee stop.

In each case, the suspect spots a female passenger wearing a valuable necklace, waits until the train is stopping at a station, then rips off her necklace, and runs out just before the doors close.

UIC students who frequently use the Blue Line stop at Harrison and Halsted said they’ll be extra vigilant in light of the recent robberies.

“It makes me pretty nervous. UIC seems like a pretty safe campus, and I think that we all like to walk around, and feel safe. So I feel like, knowing that someone’s going around snatching necklaces is kind of frightening and concerning to me,” UIC grad student Gabrielle Mitchell said.

UIC sophomore Brianna Dyer said it’s upsetting that people have to be so much more careful these days.

“I feel like I should be able to get on the train, and go home without any altercations or any problems,” she said. “For someone to rob people for something they’ve worked hard for, or something that was given to them, it’s shameful.”

Police said the suspect is a black man between 20 and 30 years old, stands 5-foot-3 to 5-foot-6, weighs 145 to 155 pounds, has a dark complexion, and a bald or shaven head.

Anyone with information about the robberies should call Area Central detectives at 312-747-8384.