Police investigating the murder of SAS officer Captain Robert Nairac in Northern Ireland more than 30 years ago arrested a man in South Armagh today.
The suspect, aged 57, was detained by officers from the Police Service of Northern Ireland serious crime branch and taken for questioning in Antrim, the force said.
Captain Nairac was abducted by the IRA, taken across the border into the Irish Republic and shot. His body has never been recovered.
Six people were convicted for their part in the killing of the army officer, who was abducted on May 14, 1977, when he visited a pub at Drumintee, South Armagh.
He was seized during a struggle in the pub's car park and taken across the border to a field at Ravensdale, County Louth, where he was interrogated for over an hour and then shot dead.
Five of those convicted were from Northern Ireland and one from the republic.
But police believe three other members of the IRA gang were involved.
It is understood two of them are now living in the United States.
Captain Nairac was working under cover at the time he was abducted.
He had been in the pub singing songs.
But suspicions were raised that it was a British military intelligence officer on the stage and he was grabbed by a gang outside.
Nairac was interrogated for several hours but he refused to break.
At one stage one of the men holding him posed as a Catholic priest in a bid to coax a confession.
Later one of the men accused of his part in the killing claimed: "He never told us anything."
Ian Paisley Jnr said: "This is a very interesting development and I welcome it.
"I look forward to the wheels of justice eventually producing justice. I just hope the police have sufficient evidence to take a prosecution and that is sufficient to get a result."
The Democratic Unionist MLA said he hoped Captain Nairac's body might be found, adding "that would be good for the family".