Teenagers used mobile phones to video a 17-year-old boy being brutally beaten and stabbed repeatedly with a broken bottle, gardaí have revealed.
Others in a large group of young people "rampaging out of control" failed to go to the aid of the victim as he lay helpless on the ground.
One horrified veteran garda said the footage of the attack was among the most shocking things he had ever seen.
The attack occurred in the Waterpark area of Carrigaline, Cork, shortly after 10.20pm on Saturday.
Gardaí are now investigating both the attack and the recording of it.
As the injured youth lay prone on the ground covered in blood, one male teenager repeatedly tried to use his phone for a close-up recording of the victim's face.
When he was chastised by a girl and urged to leave the victim alone, he loudly challenged her and demanded that another person move so he could continue recording the victim.
Footage also shows repeated attempts to stab and kick the victim.
One scene showed his clothing being pulled up in an attempt to expose his back for further stabbing attacks.
"It is one of the most shocking things I have ever witnessed," one experienced garda said. "The behaviour of some of those present can only be described as disgusting."
Sinn Féin TD Donnchadh Ó Laoghaire said the incident was "truly shocking."
"It is deeply upsetting news coming from Carrigaline last night," he said. "I am aware of videos of the incident circulating.
"Out of respect to the victim please do not share (it). Please also be aware that sharing the names of people involved in the incident could undermine chances of convictions - if you have information, please go to the gardaí.
"I wish the victim a full recovery and I hope justice will be done."
Several teenagers have been identified from the footage, as well as the youth who made the recording.
The victim was beaten and stabbed multiple times in the back and sides with a broken bottle.
It is understood the violent attack was sparked by a dispute over a mobile phone.
The young victim was taken by ambulance to Cork University Hospital, where he was treated and later discharged.
His wounds are not understood to be life-threatening, but one garda said he had been incredibly lucky to have avoided more serious injury.
It is as yet unclear whether he will require plastic surgery for some of his injuries.
A large number of teenagers are reported to have been in the area at the time, with several attempting to leave the area by bus after the assault.
A teenager who is believed to live locally was arrested in the area a short time later.
He was detained under Section 4 of the Criminal Justice Act, 1984 and was being questioned at Togher Garda Station.
Gardaí are appealing for any witnesses to this incident and for anybody with information to come forward.
They are asking road users who may have camera footage (including dash-cam) who were in the area at the time to make this footage available.
Anyone with information is asked to contact Togher garda station on (021) 4947120, the Garda Confidential line on (1800) 666111 or any Garda station.