Twelve of fifteen mobile phones belonging to senior garda officers are missing and cannot be provided to the Charleton Tribunal.
The phones were used by former garda commissioners Martin Callinan and Nóirín O'Sullivan and by former garda press officer Supt David Taylor between 2012 and 2014.
This tribunal is looking at allegations in a confidential disclosure from Supt Taylor that he was directed by former garda commissioner Martin Callinan to brief journalists negatively about whistleblower Sgt Maurice McCabe.
Supt Michael Flynn, the superintendent in charge of the Garda Síochána Telecommunications Unit, gave details of garda efforts to recover the devices, which may contain text messages between the senior officers concerning Sgt McCabe.
Supt Flynn said that metadata, information giving details of calls made and texts sent, was obtained from Three Ireland by Garda HQ, but the contents of text messages were not stored by the phone mobile provider.
Records going back seven years were retained by the company for audit purposes, and these were provided to an Garda Síochána as the bill payer.Landline records for the former commissioners were also retained at Garda HQ, Supt Flynn said.
Supt Taylor and Insp Liam Moroney identified the accounts containing billing information for the mobiles phones of former commissioners Mr Callinan and Ms O'Sullivan and Supt Taylor in 2017, after the Charleton tribunal was established.
In March 2017 twenty four boxes of telephone printouts were delivered to Garda HQ, containing records of 426 garda mobile phones between May 2012 and May 2014. Records relating to the officers were then extracted and supplied to the tribunal.
Of six phones used by Ms O'Sullivan during the two year period, one was recovered and handed in to the tribunal. Two Samsung Galaxy phones used outside the period under investigation were also made available.
Two out of six phones used by Mr Callinan were also recovered. None of the three phones used by Supt Taylor had been recovered.
Supt Flynn said as a result of a a fundraising appeal, a programme had been in place which handed old garda phones to the Temple Street children's hospital, and later to the Jack & Jill Foundation, after they were reset to factory settings.
He said this programme seemed to have wound down some time in 2012, but he could not establish exactly when.
Phones might be retained by officers once contact and other official data was removed and transferred to new devices, he said, as the phones might often contain personal and family photographs, Supt Flynn said. There was no requirement at the time to hand in old phones at the end of their life.
In response to questions from tribunal chairman Mr Justice Peter Charleton, John Ferry BL, representing Supt Taylor, said that it was not his client's position that phones were tampered with by Supt Flynn or anybody else.
Mr Ferry said that on one occasion, "a Whatsapp went live on his phone at a particular time and that alarmed him", and he became concerned as a result.
"Unfortunately those things keep happening," Mr Justice Charleton said. "I got two of them myself few days ago, and somebody from Australia keeps ringing me."
Mr Ferry also said that communication by text message and email from Supt Taylor to the former commissioners would concern media reports about Sgt McCabe, or notices about radio interviews or upcoming stories and queries from journalists. Supt Taylor made no reference to sexual allegations in text and email communications.
The tribunal resumes on Tuesday.