Officials also released a sketch of the offender, who is described as in his 40s, about 5'8" and 300 pounds with a medium complexion and short, black hair.
Police say the man attacked a woman as she was waiting at a CTA bus stop in the 6300-block of North Clark around 2p.m. on Thursday, May 2. Officials say the offender sat down next to the woman, grabbed her by the throat and forced her into a nearby alley where he sexually assaulted the victim.
The offender also took the woman's cell phone and credit card, police said.
"It's a tight community, everybody takes care of everybody else," Chicago Police Officer Bill Clancy said.
A surveillance camera is believed to have caught the offender and woman walking past a nearby store.
"To me it just looks like they're just walking or something, but I'm glad we've got the video from the store, can help the community," Moiz Khan, business owner, said.
"I'm sick standing here. There are so many people, so many businesses," the victim's mother said earlier this week.
The victim is a former student at nearby Loyola University where the campus officers warn students to be cautious.
"We try and encourage people to trust their gut. If you don't feel safe, you're not safe? unfortunately we have to put that message out there," Tim Cunningham, Loyola's student community liaison officer, said.