CCTV footage has been obtained of a male worker entering the prison accommodation of 'Scissor Sister' murderer Charlotte Mulhall.
The video is being examined as part of a major disciplinary investigation into claims of sexual misconduct by the worker at the Dochas Centre women's prison, which is part of Mountjoy Jail.
It has emerged that a fem-ale member of prison staff was in the cell with Tallaght woman Mulhall for 10 minutes before the worker was found "concealed" in the en-suite bathroom.
It is understood that prison authorities have launched a major investigation into the incident, but it is unclear whether the worker has been suspended.
Sources said he is likely to face "major disciplinary sanctions", possibly dismissal, if it is proved he had a sexual relationship with the murderer.
Mulhall (33) is fully co-operating with the investigation and has not been disciplined or moved out of the medium- security prison.
The matter is not yet the subject of any garda investigation.
Mulhall and her older sister, Linda, were dubbed the Scissor Sisters after their involvement in one of the most gruesome killings in the history of the State.
In October 2006, Mulhall was handed a mandatory life sentence for hacking to death her mother's boyfriend, Farah Swaleh Noor, in March 2005.
Noor, a 38-year-old Kenyan, was decapitated and his dismembered body stuffed into a suitcase which was then dumped into Dublin's Royal Canal.
Linda Mulhall received a sentence of 15 years for her part in his brutal death. Kathleen Mulhall, was given a five-year sentence for cleaning up the murder scene.
She served her sentence in Mountjoy with her daughters before leaving Ireland for Britain.
Linda Mulhall is due to be released in January.
However, her older sister, who was only 21 and pregnant when she murdered Noor, faces many more years behind bars
Ironically, Linda Mulhall has also been suspected of having sexual relationships with jail staff.
However, it is her trouble- some sister who has had most scrapes with prison authorities during her time inside.
In February 2014, she was disciplined after being caught with alcohol in her cell.
A few days later, she had a fight in a corridor with a fellow prisoner.
As a result, Mulhall was served with two disciplinary actions, which resulted in the loss of prison privileges.
In 2008, she was at the centre of controversy when it emerged she was given daily access to kitchen knives.
The Herald's exclusive photo showed the deranged killer holding a 10-inch knife to a male prisoner's throat.
In May 2015, she was locked away from other prisoners after a series of violent incidents.