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A 15-year-old “special needs” Chicago girl who was beaten by a group of people in a video posted online may also have been sexually assaulted off camera at some other point in time, police said Wednesday.

Detectives are trying to piece together basic facts about the “sick and disgusting crimes” committed against the teen, including where and when the beating took place and who was involved, Officer Jose Jara, a police spokesman, said at a news conference. He said the girl, who was taken to an area hospital where she was treated and released, told detectives that she was sexually assaulted in a separate incident.

One of the difficulties in the investigation stems from the fact that the teen was gone from her home on the city’s South Side for five days before she was reported missing by her family on Tuesday, Jara said. He said he didn’t know why the girl wasn’t reported missing for five days, and that no arrests have been made.

The initial investigation has revealed that the teen may have been invited by “so-called friends” who suddenly turned on her as they walked through what appears to be an alley, Jara said.

In the video, the screaming teen is peppered with punches by a group of girls or young women who are pushing one another out of the way in order to take part in the attack. The girl cowers and waives her arms in a desperate attempt to fend off her attackers, then falls to the ground, crying, as people nearby laugh and shout.

The video was posted by someone who describes herself in the caption as a friend of the girl, who she says has a “mental disability.”

Another police spokesman, Anthony Guglielmi, tweeted: “This is beyond disturbing to watch and this young girl deserves far better.” He later said the girl has “special needs,” but he didn’t elaborate.