CHESTER, Pa. (CBS) — A group of teens violently attacked a mentally challenged woman at random in Chester and recorded the entire incident on tape.

During the vicious attack, which was later posted on Facebook, the teens could be heard screaming obscenities and even laughing.

Police say on Thursday morning, an anonymous Chester resident alerted police of the taped incident that was apparently posted on Facebook.

The video starts as the group of teen girls are walking down Morton Avenue. Several seconds into the video, one of the girls casually walks up to the 48-year-old victim, who was sitting on her front step, and began to punch and beat the victim.

The attack then leads inside the woman’s home, at which point several other teens join in on the attack.

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In the video, it appears the teens are laughing throughout the entire ordeal, but instead of stopping, they complain of how much the woman’s home “stinks.”

Investigators say the attack lasted about 90 seconds. The video then shows the teens running out of the victim’s home.

Police believe the attack happened possibly Tuesday night just after 9.

“That’s one of the more horrific, savage attacks I’ve seen,” Chester Police Commissioner Joseph Bail said.

Police say the victim did not notify authorities after the assault, but did seek medical treatment. The victim didn’t contact police it’s believed due to her diminished mental capacity. The victim was not seriously injured.

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Bail said four of the six suspects have been arrested and all six will be charged as adults. Police do know the identities of the two girls at large. The four girls arrested are expected to be arraigned Friday morning on felony aggravated assault charges.

Anyone with information is asked to contact Chester Police.