A man arrested in connection with the investigation into the 1996 death of Raphoe cattle dealer Richie Barron was brought to Milford Garda Station to be interrogated to ensure that officers in Letterkenny would not "interfere" with him, the Morris tribunal heard.
Mr William Doherty was arrested shortly after he was named by another man, Mr Noel McBride, as having encouraged him to make false statements to gardaí investigating the suspicious death.
Mr McBride told detectives that he made the statements incriminating members of the extended McBrearty family at the behest of Mr Doherty and a Raphoe garda, John O'Dowd, Sgt Martin Moylan told the tribunal.
Sgt Moylan said Det Supt Joe Shelly told him Mr Doherty was to be arrested and questioned in Milford, after Mr McBride retracted his statements.
Asked why he was taken to Milford instead of Letterkenny, he said: "To take it away from Letterkenny, so there would be no interference by Garda O'Dowd, Det Sgt White, or Supt Lennon.
"I remember at one of the meetings Supt Shelley gave a direction, we must do this regardless of the consequences. I felt it was my duty to do whatever had to be done. The consequences were a serious issue for members of the force, particularly Garda O'Dowd."
A notebook apparently belonging to Garda O'Dowd was found in Mr Doherty's bedroom when his house was searched, the sergeant said. "It was a very significant, important matter. It reinforced the connection between William Doherty and Garda John O'Dowd."
Earlier, Ms Amanda Sloyan (25) said she was going out with Mr William Ayton at the time of Mr Barron's death. They went to see a film in Letterkenny, then he drove her home. On the way home they ran out of petrol, and Mr Ayton then towed the car home.
Mr Barron's death, initially believed by gardaí to be a hit and run, developed into a murder inquiry in which members of the McBrearty family became suspects. Complaints from the family of Garda harassment eventually led to the setting up of the tribunal.
Ms Sloyan said that Mr Ayton was driving his mother's car and it ran out of petrol while they detoured around the town of Raphoe on the way home from the cinema. They then got a lift from Mr Paul Kilpatrick to the Ayton home.
Last week Mr Kilpatrick told the tribunal he had not given a lift to anyone the night Mr Barron died. "I don't know why he would lie," Ms Sloyan said. "Maybe he was drinking and didn't want to be found out."
When Mr Ayton got home, he borrowed a car and towed his mother's car home. Ms Sloyan said she thought she steered the towed car, but she could not remember for certain.
Mr Peter Charleton SC said Mr Ayton lives outside the jurisdiction and was not prepared to come and give evidence.