One man died and at least seven men were stabbed during a concert in Dublin.
Detectives have not yet been able to identify the victim, who is believed to have died from a suspected drugs overdose at the Swedish House Mafia concert in the Phoenix Park in the Irish capital.
Elsewhere three of the injured men remain in a serious condition in hospital after the knife attack.
A 23-year-old suspect was arrested over a number, but not all, of the assaults.
More than 45,000 fans packed out the open air venue for the concert, which featured Snoop Dog, Tinie Tempah, Calvin Harris and headlined with the electronic dance music group, Swedish House Mafia.
A Garda spokesman said a man in his 20s became ill and looked for medical attention from staff at about 7pm. He was rushed to Connolly Hospital Blanchardstown where he was later pronounced dead.
"Gardai have not been able to identify this man and are asking family and friends to check that loved ones have arrived home safely from the event," he added.
Meanwhile gardai said a minimum of seven men, all aged in their late teens or 20s, were stabbed between 8.30pm and 1am.
"A number of the victims required treatment at Connolly Hospital Blanchardstown and three people continue to be treated at the hospital," he continued.
It is understood one of the men in his mid-20s was stabbed several times in the back.
A Garda spokesman said a 23-year-old man was arrested and is being detained at Blanchardstown garda station under Section 4 of the Criminal Justice Act 1984.
Several other people were also arrested during the evening for minor public order and drugs offences.
The city centre park has hosted a series of concerts this week, including the Stone Roses on Thursday and Snow Patrol and Florence & The Machine tonight.
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