Pennsylvania - Six teenagers were in custody on Friday on charges they brutally beat a neighbour on her stoop just "for fun" and then posted cellphone video of the attack on Facebook, authorities said.
Four 16- and 17-year-old girls were charged as adults in the attack on the 48-year-old woman, a crime that has shaken the struggling city of Chester just outside Philadelphia.
The girls were charged with aggravated assault, reckless endangerment, burglary and harassment. Another teen girl and a 19-year-old woman were also arrested later on Friday afternoon.
The woman, whom police described as "mentally challenged", was punched, kicked and hit with a shoe and chair, and suffered cuts and bruises but no broken bones, authorities said. Her name was not released.
The attack occurred on Tuesday at a two-story stucco house, where the woman lived, down the block from a small grocery store. No one answered the door at the building on Friday.
"It appears [to have been] just for fun," Chester police Detective James Nolan said. "There hasn't been a discernible explanation as to why."
Police Commissioner Joseph Bail Jr said the victim was doing better on Friday and was being treated for lacerations and abrasions at a crisis unit.
The Delaware County Daily Times first obtained video footage from police on Thursday.
It showed a group of girls walking down a pavement then suddenly attacking a woman sitting on her stoop. The teens follow the woman into her home as she tries to escape, taking turns punching and beating her. They quickly flee.
In the neighbourhood where the woman lives, cashier Crystal Pate said she knows two of the girls - one babysits her daughter - and said they were not bad youngsters.
"I can't comprehend it. I trust her with my daughter's life," the 29-year-old Pate said. "Obviously, they were showing off. That's not something you do for fun."
Pate said the woman regularly sits on her front stoop and sometimes curses people or asks for cigarettes.
Chester has long battled high rates of crime and poverty. Mayor John Linder said youth should understand that attacking people will not be tolerated.
"This is an egregious attack," Linder said. "It's unbearable."
Janet Purnell, 55, whose elderly mother lives down the street from the attack, said it is hard for her to understand why a group of girls would want to attack a woman like that.
"It really doesn't make any sense," Purnell said. "It's ignorant."