Eircom records obtained by gardaí in Donegal did not initially show alleged extortion phone calls made to members of the extended McBrearty family, the tribunal has been told.
Det Sgt Hugh Smith said he and Det Sgt Sylvie Henry investigated complaints about harassing and extortion phone calls made to Mr Frank McBrearty snr and Mr Michael Peoples.
The detective said Det Sgt Henry made an official request for incoming phone calls to Mr Peoples, and in the meantime Mr Pat Doherty obtained an itemised bill from Eircom, showing calls from his home to Mr Peoples. Mr Doherty's son, William Doherty, is a police informer.
However, two requests to Eircom came back showing that no calls had been made to the Peoples home on the date in question.
"Pat Doherty, from whose house the calls were made, had got his own itemised bill and the calls came up on his bill," Det Sgt Smith said.
Tribunal barrister Mr Peter Charleton said that Eircom records twice showed no incoming calls, and that a third request showed calls made from the Doherty home, but not a call from the home of Garda John O'Dowd.
The barrister said the Carty team also had problems with Eircom, and tribunal agents were investigating evidence from the company showing phone calls to the Peoples were "completely erased" for a period.
Earlier the tribunal heard that pages were missing from the Garda correspondence book covering the investigation into the death of Raphoe cattle dealer Mr Richie Barron.
Tribunal barrister Mr Anthony Barr said the first 20 pages of the book were missing, as were pages 25 to 29.
"I must say it is a complete surprise to me, I didn't realise the pages had gone missing," said Sgt John O'Toole, who worked in the incident room managing the investigation.
"It would be as clear as day that the first 20 pages are missing," Mr Barr said.
The sergeant said the first pages in the book might have been used for another case, but said he couldn't offer an explanation for the other missing pages.
The first record in the correspondence book was on October 18th, 1996, four days after Mr Barron died. Entries between November 1996 and February 1997 were also missing.
During this period a vital statement was taken from Mr Noel McBride, described as the "catalyst" that led to the arrests of 12 people in December 1996.
In September 1997, Mr McBride withdrew his statement.