He is accused of being involved in the sex assault, which was streamed live and removed.
The woman then reported her daughter missing, and on March 21 she approached Johnson as he was leaving a police station in the Lawndale neighborhood.
It is believed that five or six individuals took part in the disgusting attack against the teen girl; however, investigators have declined to comment on how many individuals they are still looking for.
The boys in custody were ordered held in juvenile detention pending trial on charges of criminal sexual assault and distributing child pornography, according to a spokeswoman for the Cook County State's Attorney's Office.
"Both videotaped these egregious actions", Gardner said.
Assistant public defender Liliana Dago said prosecutors hadn't proven probable cause for the 15-year-old, particularly on the child pornography charge.
Police were able to identify two of the teens responsible using social media search warrants which they obtained with the help of Facebook.
A second teenager suspected in the sexual assault of a Chicago teenager that was streamed on Facebook Live turned himself in to police on Monday afternoon.
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"She is truly traumatized but detectives are incredibly inspired and motivated by her strength and courage", he wrote, adding that "several young men" are still sought by police in the case.
"We've seen a couple acts in this city now in the last few months involving social media, and it just disgusts me that people could look at those videos and not pick up the phone and dial 911", Johnson said at a news conference on Sunday.
The AP generally does not identify potential victims of sexual assault and is not identifying the mother so as not to identify the girl.
"It makes me wonder, where are we going, what are we doing as a society?"
Officers found the girl in the street the next day and she was taken to a hospital and reunited with her mother. Crisis responder Andrew Holmes is in touch with the girl's family.
The taunts prompted authorities to relocate her family to another home, described by Guglielmi as "a safe place".
Guglielmi said Johnson was "visibly upset" after he watched, both by the video's content and the fact that there were "40 or so live viewers and no one thought to call authorities".