Two men are still being detained in Limerick in connection with the murder of Roy Collins on Thursday.
Garda chiefs, who have drafted in more than 200 extra officers to fight gang crime in Limerick over the past two years, said they will spare no resources in bringing those responsible for the latest killing to justice.
Roy's father Steven Collins said he believes his son was targeted because his family gave evidence in court four years ago against Limerick criminal Wayne Dundon.
He is calling for tougher measures to tackle gangland crime.