The trial of five care workers charged with assault at the Áras Attracta residential centre in Co Mayo has begun at Castlebar District Court.

The five each face a single charge of assault on dates in November 2014.

The proceedings follow a report by the RTÉ Investigations Unit on care standards at the Swinford centre.

The State called the head of the investigations unit, Paul Maguire, as its first witness.

Mr Maguire outlined how footage was obtained at Áras Attracta and the process that led to it being collected each day by an undercover reporter.

The trial is expected to take a number of days to complete.

He was asked to outline how hidden cameras recorded interactions between staff and residents at Bungalow 3 in Áras Attracta.

The court heard that footage was gathered on a fixed camera in a common room there between 3-19 November 2014.

This was transferred to a hard drive each day. The master copy containing 190 hours of material was then replicated for use by those working on the television programme.

It was subsequently copied onto another hard drive after gardaí requested the footage for their investigation.

Legal representatives for the five care workers questioned Mr Maguire extensively on the manner in which the footage was gathered and stored.

A second witness, RTÉ producer Janet Traynor, told the court that a total of six video files recorded on 12 November were deleted on her instruction.

She said these were all recorded inadvertently, five had just a black screen when viewed and the sixth featured an empty common room.

Legal teams for the defendants have focused on the issue of deleted files and there have been extensive exchanges relating to when the State became aware of this, as well as the clarity provided by RTÉ witnesses in this regard.

Defence legal teams queried why Ms Traynor had given a statement to gardaí saying she was 99% sure no footage had been deleted.

Ms Traynor said she had not been 100% certain and had reviewed the matter before giving evidence.

Under cross-examination by barrister Connall MacCarthy, production assistant Pauline Dunne said she too had only realised that she had deleted the six files in question after checking the situation in recent weeks.

The undercover reporter who placed a hidden camera in Áras Attracta has also been giving evidence.

Caoimhe Delaney told Patrick Reynolds, BL for the State, that she secured work experience at Áras Attracta and first brought a fixed camera into a sitting room there on 3 November 2014.

Over the following 16 days material was filmed using two alternate cameras.

She told Conall MacCarthy, barrister for one of the accused, that she never interfered or edited the footage on the camera and added that this was not possible.

Ms Delaney told Eoin Garavan BL that nobody in the HSE or in Áras Attracta assisted her in any way.

Ms Dunne told the court that she was in charge of collecting the footage, logging it and making all the copies that were required.

She would meet Ms Delaney each day between 9am and lunchtime at Áras Attracta and collect the camera from her.

She would also give her a replacement camera which would be fully charged.

Ms Dunne said she would have checked that date and time settings were correct. She would also check that motion and audio sensors were working properly.

This would ensure the camera would start recording in the event of movement or sound being detected.

Ms Dunne would then transfer the filmed material onto a master hard drive before deleting the footage on the camera so it would be ready to be used again on a subsequent day.

Clips were initially recorded in 15-minute segments but due to the volume of material, this was later extended to allow for half-hour clips.

RTÉ is giving defence teams access to the original master hard drive overnight.

The case resumes in the morning.