Four people are being questioned in Limerick as part of a murder investigation into the death of Mr Anthony O'Donoghue earlier this month.
A Garda spokeswoman said the people were arrested at 8.05 a.m. She said they are being questioned and no charges have been made yet.
The Garda launched a murder inquiry after the death of Mr O'Donoghue (26) who died on March 5th due to head injuries, two weeks after being assaulted.