Legal experts have said that an independent panel of doctors and experts will be tasked with deciding whether John Gallagher ought to be further detained, following his return to the Central Mental Hospital.
Mr Gallagher absconded while on day release from the Central Mental Hospital in 2000, after being found guilty but insane on a charge of murdering Anne and Annie Gillespie in the grounds of Sligo Hospital in 1988.
His extradition to the Republic was never sought, because under the law, he was never convicted of a crime in Ireland.
Gallagher, a native of Lifford in Co Donegal, shot the women, aged 51 and 18, when he was 22 years old.
He walked back into the mental hospital in Dublin earlier this month.
It is reported that he is planning to take a legal case to be declared sane again so that he can be released.
Speaking on RTÉ’s News at One, Senior Council Paul Anthony McDermott said that under previous legislation, the decision as to whether to further detain or release a patient in such circumstances would have been made by the Minister for Justice.
However, Mr McDermott said that a new system was put in place as a result of the Mental Health Act 2006.
"Mr Gallagher's position has changed now. At the time of his escape he was subject to the Minister for Justice, who could decide whether he could be released,” Mr McDermott said.
“But now he is going back to a very different regime, because now he can go before an independent panel of doctors and experts."
He continued: “If that independent body says that now Mr Gallagher has been cured, that his mental health problems, whatever they were, have been cured, then there is no basis for detaining him any further because the only basis on which he is being detained is that he is mentally ill.
“If the doctors say he isn't, then he walks free, and from his point of view, that's the end of the matter."
Mr McDermott’s comments were backed up by Aine Hynes, who is a solicitor and Chair of the Irish Mental Health Lawyers Association.
Speaking earlier on Today with Pat Kenny, Ms Hynes said the provisions of the Mental Health Act 2006 would apply retrospectively in a case such as John Gallagher's.
"Effectively, there is the power to bring somebody back if they have breached their conditions of temporary leave," Ms Hynes said.
"Now, in this sort of situation, what would happen is the review board would review the patient concerned and then they would make an order for continued in-patient treatment if they saw fit, or for discharge on conditions or unconditionally."
John Gallagher was found "guilty but insane" in relation to the murders of Anne and Annie Gillespie.
According to Ms Hynes, that verdict has been replaced with that of "not guilty by reason of insanity" as a result of the 2006 Act.
