The murders of Sylvia Sheils (58) and Mary Callinan (61) in March 1997 were shocking, not just for the fact that two people were killed, but also for the viciousness of the attacks.
The two women, who were living in sheltered housing in Grangegorman, linked to the nearby St Brendan's psychiatric hospital, were found with 30 stab wounds each from what appeared to have been a frenzied attack.
Gardaí from the Bridewell Garda station mounted a huge murder investigation involving 200 officers. Four months later, in July, gardaí arrested a 24-year-old homeless man, Dean Lyons, who had been seen in the Grangegorman area around the time of the murders.
Lyons had a serious drug problem and was well known around the Grangegorman area.
He made a full confession to the killings and was charged on the advice of the Director of Public Prosecutions. He was remanded in custody.
Just a fortnight later, less than six months following the Grangegorman killings, gardaí found themselves investigating another double murder, this time near Castlerea in Co Roscommon.
A young Dublin couple, Carl and Catherine Doyle, were found murdered in their rural home in what was another frenzied knife attack. Catherine's sister, Sarah, who had been visiting for the weekend, was also found seriously injured in the remote house.
Her boyfriend, Mark Nash, who was missing, quickly emerged as the prime suspect.
Nash, born in Mayo in 1973, had spent most of his life in England, and moved to Dublin in 1995. He had a history of violence.
He was arrested in less than 24 hours just outside Galway city.During his interview, he also confessed to the two murders in Grangegorman, although he subsequently retracted this confession. Despite the confession, which was relayed to senior officers in Dublin, Lyons continued to be held on charges relating to the Grangegorman murders.
It was not until March, seven months later, that the DPP decided to drop the charges against Lyons, and he was released. He died in Manchester in September 2000 from a drug overdose.
Meanwhile, Mark Nash was convicted and sentenced to two life terms for the murders of the Doyle couple. The case was the subject of an internal Garda inquiry, the results of which have never been published.
Nash has been referred to as a suspect in the Grangegorman murders during the inquest into the deaths of Sylvia Sheils and Mary Callinan in 2002.
Last year he also took High Court proceedings against a decision by the then minister for justice, Mr John O'Donoghue, to refuse a request to be transferred to an English prison.
Last November the High Court found Mr O'Donoghue had acted reasonably in his refusal.