The Disclosures Tribunal has heard that only three out of 15 mobile phone handsets used by former commissioners Martin Callinan, Nóirín O'Sullivan and former head of the garda press office, Superintendent David Taylor, have been recovered and handed over to the inquiry.

A total of 12 phones, used in the period of interest, have gone missing and cannot be located.

Superintendent Michael Flynn of the Garda telecommunications unit gave evidence this morning that because of the missing handsets, the content of some text messages cannot be recovered.

However, details of phone calls and outlines of texts sent to particular numbers are available.

He said the "billing event" of a text was available but not the content of the text itself.

The inquiry is examining the telecommunications usage of the three individuals during the period when Supt Taylor was head of the press office from July 2012 to May 2014.

One of Ms O'Sullivan's six phones was found, two of Mr Callinan's six phones and none of Supt Taylor's three handsets.

Counsel for the tribunal, Diarmaid McGuinness, said people might think it strange that so many phones had gone missing.

Supt Flynn said there was not a policy of handing in old phones at that time and devices were considered obsolete when replaced.

The tribunal has heard that some phones may have been given to the Jack and Jill Foundation.

However, Supt Flynn said that no log was kept of phones donated so there is no evidence tracing particular phones.

He said they were just "factory reset" and thrown in the Jack and Jill box.

Supt Taylor's lawyer said the superintendent is not alleging that the smear campaign against Sgt McCabe was conducted by text.

The inquiry also heard that Supt Taylor is no longer alleging his phone was tampered with. Instead, he says he became concerned when a WhatsApp invitation went live and "alarmed him".

The inquiry has concluded for today and will resume on Tuesday.