Incompatible telephone systems meant that joint RUC/Garda meetings were set up over unsecured lines, the tribunal looking at allegations of Garda collision in the deaths of two senior RUC officers heard.
Retired garda superintendent Pat Tierney told the Smithwick inquiry he also had concerns about the number of times that RUC Supt Bob Buchanan travelled to Dundalk using the same car.
Buchanan and his colleague, Chief Supt Harry Breen, were killed in an ambush a few hundred yards north of the border as the returned from a meeting in Dundalk on 20 March 1989.
Mr Tierney said he was told there was a message to call Supt Buchanan when he got to work that morning, and when he got in touch he learned that Buchanan wanted to arrange a meeting with Garda Chief Superintendent John Nolan.
The call was made over an open line because “Armagh did not have a secure element similar to Dundalk,” he said.
Mr Tierney said he spent the morning on an inspection of border crossings, and found out that Breen and Buchanan were in Dundalk shortly before he returned to the station.
He said that around 3pm he met Superintendent Buchanan, who was “joyous” about a transfer to a new position the following month.
Buchanan shook hands with Tierney, and said they would meet again before his transfer.
“He then left my office and I did not see him, after hat,” Tierney recalled.
A couple of hours later, an RUC officer called Tierney and asked “have our boys left yet? There’s an incident at Meigh (a border village). We’re worried.”
Tierney and another Garda then travelled to the border, from where they were able to see Buchanan’s car, and “assumed the worst.”
The tribunal also heard that the car park at Dundalk garda station was open to the public, and was often used as a shortcut between two streets in the town. In addition, Superintendent Buchanan often parked his car at the front of the station.
But Tierney said he had “no evidence” that any Garda or civilian working for the force leaking information to paramilitaries, and said that any cross-border meeting would be known only to “a very tight circle” in the station, consisting of the Chief Superintendent, the Superintendent, and one of the Inspectors.
He said that in the month before Buchanan’s death, he had met with him “a good seven times” in Dundalk, and three times in Northern Ireland.
The tribunal resumes on Tuesday 21 June.