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A 14-year-old boy has been arrested in the sexual assault of a 15-year-old Chicago girl that was streamed live on Facebook and watched by about 40 people who didn't report it to authorities, police said late Saturday.

Chicago police officials on Sunday said more arrests are expected as the investigation continues, including of a 15-year-old whom police have an arrest warrant for.

Authorities have said the attack involved five or six males, and police spokesman Anthony Guglielmi said the 14-year-old boy "was one of the offenders in the video."

Guglielmi said the boy under arrest faces felony charges of aggravated criminal sexual assault, manufacturing of child pornography and dissemination of child pornography.

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The spokesman has said police were not aware of the mid-March attack until March 20, when the girl's mother approached Superintendent Eddie Johnson as he was leaving a police station on the city's West Side and showed him the video.

BREAKING - Tonight, CPD arrested 1st of several juvenile offenders in Facebook sexual assault incident. Press conf Sunday at 11am @ CPD HQ pic.twitter.com/3qdgpecoVI — Anthony Guglielmi (@AJGuglielmi) April 2, 2017

Detectives located the girl on the street a day after her mother reported her missing and she was transported to the hospital, Area Central Detective Commander Brendan Deenihan said at a press conference Sunday. He said the girl knew one of the offender and was lured into a residence located in Chicago's west side.

"From there, she was not allowed to leave and didn’t consent to what occurred," he said.

Multiple warrants for social media data have been executed, Deenihan said, adding that detectives are still going through online posts to identify "several other offenders." Deenihan did not know whether anyone who viewed the video would be charged.

Communicating with the traumatized victim has complicated the investigation, Deenihan said. He noted that the girl has been getting bullied on social media.

"We have a very good idea of who these individuals are, but working with this victim at this time is very, very slow. She’s traumatized. She’s going to need help for a long time after this," Deenihan said.

Chicago Police Superintendent Eddie Johnson. Scott Olson / Getty Images

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," Guglielmi said.

The girl's mother last month said that her daughter received online threats following the attack and that neighborhood kids were ringing her doorbell looking for the girl. The Chicago Sun-Times later reported that the girl's family had been relocated.

"No woman should ever be treated the way this young woman was," said Johnson on Sunday. "The young men responsible, they should be ashamed of themselves, they humiliated themselves, they humiliated their families."

The video marks the second time in recent months that Chicago police have investigated an apparent attack that was broadcast live on Facebook. In January, four people were arrested after video showed them allegedly taunting and beating a mentally disabled man.

"We've seen a couple of acts in the last few months and it disgusts me that people would look at those and not pick up the phone and call 911," Johnson said at the press conference. "Where are we going in society?"