Serial killer Mark Nash has begun his appeal against his convictions for a double murder in Grangegorman in Dublin in March 1997.

Nash, who's originally from England, was convicted two years ago but has raised a number of issues about the way the trial was run.

A the time of his conviction, he was already serving a double life sentence for murdering two people in Co Roscommon

Following a 48-day trial in April 2015, Mark Nash was found guilty of the murder of Sylvia Shiels and Mary Callanan, whose mutilated bodies were found in their sheltered accommodation in Grangegorman in Dublin 20 years ago.

He was arrested in August 1997 on suspicion of murdering a couple in Roscommon.

And while in custody, his trial heard he made a number of admissions in relation to the Grangegorman murders five months beforehand.

Opening his appeal today, Mark Nash's barrister Hugh Hartnett described this case as "unusual and extraordinary".

His client, who has grown a dark beard since his last court appearance, took notes in the dock behind him.

Mr Hartnett said it was unusual because another man called Dean Lyons admitted killing Ms Shiels and Ms Callanan, but he died while in custody in the UK in relation to another matter.

The garda investigation then hit a wall until 2009 when scientific advances led to the discovery of DNA on a jacket seized from Nash which linked him to the Grangegorman murders.

During the trial, it emerged the jacket was examined in the same lab where some bed clothing from the crime scene was brushed down.

Experts told the jury there was a possibility of cross-contamination but Mr Hartnett feels the judge didn't adequately deal with the issue.

He also accused him of inviting the jury to speculate in relation to the admissions made by Dean Lyons.

He has also raised issues about Nash’s detention and the admissibility of the admissions he made while being questioned about the Roscommon murders.

The hearing is due to take three days.