Ronald Macon, 35, has confessed to three recent murders and is linked to the killings by DNA evidence, according to police.
He has been imprisoned in the Cook County Jail since August for an unrelated sex crime.
Of the 16 original murder cases, nine murders and three sexual assaults dating back to 1995 remain unsolved.
Macon is to appear in court Tuesday.
Police Commander Frank Trigg said police obtained a videotaped confession from Macon.
"Once we had a chance to speak to him, his status escalated to that of a suspect," Trigg told WBBM.
The three women were killed this year. Angelnetta Peeples, 43, was found Feb. 20. She had been strangled and hit in head. Linda Soloman, 36, who was found April 14 in a stairwell, also had been strangled and hit in the head. Rosezina Williams, 50, was found strangled in a dumpster on June 21.
Macon was being held on a $1.25 million bond for the previous rape charge.
Charged with three counts of murder, he could face the death penalty if convicted, authorities said. They said they might also charge him with rape.
Police had been frustrated in finding suspects in the string of killings despite the DNA evidence. Few in their neighborhoods knew the women or were willing to talk to police.