Gardaí and members of the National Bureau of Criminal Investigation arrested four people over the murder of Kieran Keane and the alleged kidnapping of brothers Kieran and Eddie Ryan in January.
The four, three men and one woman, were arrested this morning in the Thurles area and are being questioned at Garda stations in Limerick.
The four are being held under Section 30 of the Offences against the State Act. They can be detained for 24 hours; that can be extended to 48 hours.