A garda superintendent has denied at the Disclosures Tribunal that he deliberately ignored a HSE letter in order allow a false sexual abuse allegation made against Sgt Maurice McCabe to fester.

Supt Noel Cunningham investigated the original 2006 abuse complaint and concluded there was no ground for prosecution.

The Director of Public Prosecution dismissed the allegation.

The tribunal is examining whether a false version of that complaint was used by senior gardaí to discredit Sgt McCabe.

The tribunal heard that the Health Service Executive wrote to Supt Cunningham in August 2013 when the sexual abuse complaint resurfaced, to check if it was the same as the 2006 one.

Supt Cunningham did not reply although he did receive the letter when he returned from leave in September 2013.

He told the tribunal he regretted not replying and that he should have dealt with it.

SC Patrick Marrinan for the Tribunal suggested to Supt Cunningham that perhaps he deliberately ignored the letter because that would allow it to fester and surface later to cause Sgt McCabe some hardship.

Supt Cunningham denied that was the case; he said he simply forgot to reply.

He said his actions were not malicious and the reason he forgot about the letter was because he was being too careful and he had filed it away.

He said he did not accept that the subsequent "debacle" would not have happened had he replied.

He said the HSE already had the information.

The tribunal heard that the relationship between Sgt McCabe and Supt Cunningham had become strained after the 2007 investigation.

Supt Cunningham agreed that Sgt McCabe had become a thorn in his side and he said Sgt McCabe had an input into complaints made against him, which were investigated by Sgt Tony Byrne and Supt Leo McGinn.

The tribunal heard that at one point Sgt McCabe secretly taped a conversation between himself and Supt Cunningham.

Supt Cunningham said what happened during the conversation was unsettling.

Supt Cunningham said the investigation into Maurice McCabe changed the sergeant and that afterwards he trusted nobody.