A man who died in custody was arrested twice by gardai investigating the suspected murder of missing teenager Ciara Breen.
The Herald can reveal that Liam Mullen, who was the chief suspect in the teenager's disappearance, died of a suspected overdose in Dundalk Garda Station.
The 55-year-old was detained on Thursday evening at around 8.30pm in the town centre on suspicion of drink-driving, and swallowed a substance before his arrest.
While being held in the nearby garda station he became ill at around 10pm and an on-call doctor was requested to attend the barracks. Despite efforts by the doctor to resuscitate him, Mullen was pronounced dead later that evening.
An investigation has now been launched by the Garda Siochana Ombudsman Commission (GSOC). A post-mortem examination was expected to be carried out on the deceased last night, which will help GSOC with their investigation.
"At this stage GSOC continues to examine matters under S.91 of the Garda Siochana Act 2005," a statement last night said.
Sources said an overdose is being treated as the cause of death in the initial stages of the investigation.
"There is nothing to suggest that Garda misconduct led to this individual's death," the source said.
Mullen was the chief suspect in the disappearance and suspected murder of Ciara, who was 17 when she was reported missing on February 13, 1997. The teenager has never been located and gardai suspect she was murdered.
Ciara's mother, Bernadette, was last night too upset to comment.
Although he was never brought before the courts in relation to her disappearance, sources revealed Mullen would have been charged with Ciara's murder if her body had been located.
Mullen was first arrested over the disappearance in 1999.
He was arrested again in 2015 after gardai received two letters and took statements from two people who came forward with fresh information. He was later released without charge. Mullen had always maintained his innocence and said he had no relationship with Ciara other than to say 'hello' to her.
A number of files were sent to the DPP in relation to the case but no charges were ever brought.
Mullen resided at a property on Bachelor's Walk, Dundalk, which is located just yards from the home of Ciara's mother.
On the night of her disappearance, Ciara told her mother she was going to bed. However, she snuck out of the house to meet someone and was never seen again.
Gardai believe Ciara was murdered on the night she went missing, but they have never found her body.
Ciara's friends told gardai at the time that she had made arrangements to meet Mullen, who was almost twice her age, that night.
They claimed he had approached Ciara and her friends on the day before her disappearance and they overheard her making arrangements to meet him later that night. He denied the conversation ever took place.
After her disappearance, lands linked to Mullen and his family were searched, but nothing of evidential value was found.
Despite her disappearing more than 20 years ago, gardai gathered valuable information in recent years on the case.
This included two anonymous letters which led to a fresh search for the teenager being carried out in 2015 at Balmer's Bog. Nothing significant was located.
In December 2014, Ciara's mother Bernadette appealed for anyone with information to come forward.
"I had just one little girl, my heart, my soul, my world. And just like that she was gone.
"She was not streetwise and she paid the price. And if anything comes out of this I would like it to be for whoever has the information we need for Ciara to give it," she told RTE's Crimecall programme.
"Please, please, don't let her lie out there on her own any more, let her come home."