A man has been charged in connection with a number of stabbings at a gig in Dublin's Phoenix Park.
Nine people are thought to have been stabbed during the open-air concert, which was headlined by dance act Swedish House Mafia.
In a separate incident, one man in his early 20s died from a suspected drug overdose.
The 23-year-old man was arrested at the venue and charged in relation to at least four of the attacks.
The other five were injured during a brawl involving broken bottles and knives.
Three of the stabbing victims remain in hospital, with two of them in a serious but stable condition. It has not been established if all of the stabbings were carried out by one individual or a number of people.
Gardaí said more people may have received minor injuries in the spate of attacks and urged them to come forward to help with their inquiries.
The sister of one of the victims told the Irish Independent: "He was just watching the show when someone came up and stabbed him four times in the back. He didn't know the guy. He can hardly remember it. He said it was all a blur.
"Two other guys who are on his football team were also attacked but he wasn't at the concert with them."
Denis Desmond, managing director of concert promoters MCD, said: "Ticket holders entering the site were subject to a search permissible by law.
"Every precaution, as far as possible, was taken to ensure the safety and security of the audience at all times.
"Despite our best efforts - with security and gardaí personnel levels well in excess of the required numbers for a licensed event of this size - there is only so much one can do to combat anti-social behaviour."
According to Desmond, more than 45,000 fans attended the event, which featured performances by Snoop Dogg and Calvin Harris.
More than 30 arrests were made at the concert for offences ranging from public order breaches to assault and possession of drugs.