Cortez Foster, 41, is charged with aggravated battery, aggravated sexual assault and armed robbery.
The victim, a suburban Schiller Park man, was found wandering Grant Park after someone called 9-1-1 to report a bloody-faced man with no shoes or pants staggering down the street. He had been badly beaten and sexually abused.
Word of the attack has left some who live or work in Chicago's South Loop neighborhood shaken.
"It is kind of shocking to hear that something like that would happen in this area, you know? It makes you just kind of wonder, what's really going on with our city?" said Beryl Armstrong, who works in the South Loop.
Police say the brutal beating happened early Saturday morning just after 12:15 a.m. not far from Grant Park's General Logan monument.
Responding officers say the 65-year-old northwest suburban man was unable to speak and suffered severe injuries when he was battered with a tree branch. His cell phone was also taken.
The Pavelics are staying at a hotel along Michigan Avenue while visiting from Milwaukee, Wisconsin, and were shocked to learn of the violence.
"We don't have any concerns," said Peter Pavelic. "We just got here yesterday, and just walking around, and everyone's been really friendly."
Monday afternoon, Belmont Area detectives continued to interview Foster who was initially brought in for questioning as a witness but arrested late Sunday night.
The 45-year-old is a convicted felon who was paroled in May of 2010 for armed robbery after being sentenced to 20 years in prison in March 2001.
According to published reports, Foster also has two other convictions on his record, a six-year sentence for robbery in 1996 and a seven-year sentence for a 1991 armed robbery conviction.
Detectives are still gathering details about the attack and have offered no motive for the beating.
"My concern is, with that occurring right here, they need to have some control, some police visibility or something, because that's a wake-up call," said Lavette Callahan, who works downtown.
Detectives are looking into the possibility there was some surveillance video from the area that may have captured the crime on camera.