Elite Dublin detectives sent to Donegal during the investigation into the death of cattle dealer Mr Richie Barron challenged the account of suspended Det Sgt John White yesterday.
He claims they travelled to Derry with him following controversial arrests of members of the extended McBrearty family in Raphoe.
Ms Seán Quinn BL, challenged Det Sgt John White's evidence that he met Det Sgt John Melody - a member of the National Bureau of Criminal Investigation (NBCI) - the night Frank McBrearty jnr allegedly made a statement of admission while under arrest, and that four NBCI members travelled to Derry together the next day.
"They're four liars if they say that. They went in my car, a green Rover," said Det Sgt White, who said he travelled to Derry with Det Sgt Melody, Det Sgt Eamon O'Grady, Det Sgt Gerard McGrath and Det Garda John Fitzpatrick.
However, Ms Quinn said the four Dublin detectives left Donegal for Dublin by 1pm on December 5th, and so could not have travelled to Derry.
Det Sgt White said he was not sure of the date of the trip.