A 14-year-old boy has been arrested and charged with the sexual assault of a 15-year-old girl that was streamed live on Facebook.
The teenage girl, from Chicago, was allegedly assaulted by five or six males as around 40 people watched on the video streaming service without reporting the attack.
Chicago police spokesman Anthony Guglielmi said the juvenile suspect faces felony charges of aggravated criminal sexual assault, manufacturing of child pornography and dissemination of child pornography.
"Additional arrests are expected as the investigation continues," Mr Guglielmi said.
Mr Guglielmi has said police were not aware of the attack until the girl's mother approached Police Superintendent Eddie Johnson as he was leaving a police station on the city's West Side and showed him the video.
Mr Johnson was "visibly upset" after he watched, Mr Guglielmi said, both by the video's content and the fact that there were "40 or so live viewers and no one thought to call authorities."
Police have said the attack involved five or six males.
The girl's mother told The Associated Press last month her daughter received online threats following the attack.
The Chicago Sun-Times later reported that the girl's family had been relocated.
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.
Additional reporting by Associated Press