On Sunday, Deenihan said police were investigating what he called "social media bullying" and that detectives have "executed social media search warrants" in the case. A 14-year-old boy faces charges of aggravated criminal sexual assault and making and disseminating child pornography.
A spokesperson for the Chicago police said, Anthony Gugliemi confirmed that the arrested boy was one of the offenders identified in the video, which was later taken down from Facebook.
Police have said the attack involved five or six males.
Johnson was initially approached on March 21 by the girl's mother, who was "desperately seeking help".
Chicago Police Superintendent Eddie Johnson plans to give a press conference Sunday afternoon to give the public more details.
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The teen was treated at a hospital after the assault before returning home to her family.
This is the third such incident in recent months in Chicago that has been broadcast live on Facebook. "They've humiliated themselves, they've humiliated their families, and now they're going to be held accountable for what they did".
Last month, the girl's mother told The Associated Press that her daughter received online threats following the attack and that neighborhood kids were ringing her doorbell looking for the girl, who hasn't returned to the neighborhood. "Of course I didn't grow up with social media".
Police touted the numbers as a continuation of February's slight downward trend in violence, when 210 people were shot, 46 of them fatally.
In the video the girl could be seen being assaulted by several young men who also appeared to be teenagers.
"We take our responsibility to keep people safe on Facebook very seriously and will remove videos that depict sexual assault and are shared to glorify violence".
In July, Facebook acknowledged that while live video can be a powerful tool to document events, sharing - and allowing - videos on the platform must be done responsibly.
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