A Tusla social worker has said there may have been a cover up when a file on garda whistleblower Sergeant Maurice McCabe was sent to her to review, as key documents were missing.

The absent material related to the error made by incorrectly inflating a historic sexual abuse allegation made against the Sgt McCabe, to a more serious rape accusation.

The tribunal is examining allegations of a senior garda smear campaign against Sgt McCabe and is hearing from one witness who was unable to give evidence in July.

Lisa O'Loghlen of Tusla's sexual abuse regional team (Sart) was given the McCabe file to review in July 2016. 

At that stage, Sgt McCabe had been told in a letter about the incorrect allegation and his solicitors had responded disputing the accusation and asking how the mistake had come about.

Ms O'Loghlen confirmed that key documents relating to the garda notification of the incorrect allegation and the correction later made, were missing from the file.

Patrick Marrinan SC for the Tribunal suggested that someone deliberately removed elements in order to cover up substantial error. 

He said it looked as though those involved in making "error after error" in 2014, had removed documents.

Ms O'Loghlen said there may have been a cover up but she could not say who might have been involved.  She also suggested that it might be possible that the documents were not originally put on the file.

Mr Justice Peter Charleton said that when the Tribunal got the file, all the documents were on it and that was a very stark set of facts.

Ms O'Loghlen said she could see how a cover up may have happened but she could not point the finger at people. She said the file was very poorly managed.