The chairman of the Garda Síochána Ombudsman Commission (GSOC) said he suspected the organisation's office was under some sort of surveillance.

Simon O'Brien also told the Oireachtas Committee on Public Service, Oversight and Petitions that officials within the Ombudsman's office believed the threats could have come from An Garda Síochána itself. However, he stressed there was no evidence of surveillance by the Garda.

While he regretted not informing Minister for Justice Alan Shatter of the suspected surveillance, Mr O'Brien said he made a "strategic decision" not to do so. "The level of public disquiet in allegations that gardaí might be involved in any kind of that activity was immense," Mr O'Brien said.

Disclosing the information “had immense potential for further damage to what was already a strained relationship” between the GSOC and the force.

He added that the GSOC’s director of investigation believed last October that threats came from the Garda.

Mr O’Brien also said he must put a “member of An Garda Síochána in the suspect group” of those who may have carried out any surveillance.

However, he also suggested there may be an "internal mole" within the GSOC.

'Rogue member'

He said he “certainly suspects we may have been under some form of surveillance”.

GSOC commissioner Kieran Fitzgerald said it would have been "ludicrous" to go to the Garda with something that may have involved some of their members, while Mr O'Brien said "it could be an issue of a rogue member".

Mr O’Brien said the decision to carry out a security sweep of the GSOC’s Dublin office “came from nothing more” than the idea that risks of a security breach were increasing and that the GSOC needed to be aware of risks.

The threats discovered were on the "higher level of suspicion" but in response to questioning from Fianna Fáil justice spokesman Niall Collins, Mr O'Brien said he was confident the GSOC's casework had not been compromised. "There is a very, very small chance that this could be some innocent telephone call coming in," Mr O'Brien said.

The context for the sweep was a higher public profile for the GSOC because of its differences with An Garda Síochána. A group of only four or five people were aware of the sweep initially. "We kept the security sweep to a very tight group of individuals, I think no more than four or five."

'Leaked report'

Mr O’Brien said he “strongly suspects” a section of a report on the sweep, which he had in his possession since before Christmas, was given to a journalist.

He said the initial story in the Sunday Times newspaper had a strong basis but claimed there were inaccuracies in the confidential GSOC report.

“I have looked at that document and that does not fit a recollection I have,” Mr O’Brien said. He also said more details from the report which dealt with the rationale for the sweep could be published in the coming days.

“It is highly likely that information has come from documents within GSOC,” he added, with “less than seven” people having access to the documents.

“It could be that the person who leaked this report is responsible for other issues.”

However, he said the confidential report may make reference to reasons "for the sweep that do not accord with my recollections". He also regretted Mr Shatter and Garda Commissioner Martin Callinan had been "blindsided" by the controversy and said he would be furious if in Mr Callinan's position.

Mr O’Brien met Mr Callinan earlier this week to discuss how the GSOC and the Garda could move on, and said he considered his own position before he went to meet Mr Shatter on Monday.