A man was arrested today by detectives investigating the brutal murder of south Armagh man Paul Quinn.
Mr Quinn, 21, from Cullyhanna, was beaten to death by a gang in an isolated barn in Co Monaghan in October 2007.
Gardai said the latest suspect was arrested in Co Louth early this morning.
The man, in his mid-30s, is being detained at Carrickmacross garda station under Section 30 of the Offences Against the State Act.
Seventeen people have been arrested in connection with the cross-border investigation by An Garda Siochana and the PSNI.
Mr Quinn was lured into a cattle shed close to the Irish border and beaten to death.
He died from multiple injuries, due to blunt force trauma.
Paramilitary ceasefire watchdog the International Monitoring Commission (IMC) said those behind the murder were either former Provisional IRA members or associates.