MacArthur, 66, was granted temporary release from Shelton Abbey on Monday, with his status under rolling review by the probation service.
He had served 30 years for the violent murder of nurse Bridie Gargan in Phoenix Park in 1982. He was also charged with the shooting dead of Co Offaly farmer Donal Dunne, but that case never made it to court.
Speaking in Dublin yesterday, John Lonergan said MacArthur may have been released before now had there not been a fear within political circles of being seen to be “soft on crime”.
“Malcolm MacArthur had a very high profile from day one,” said Mr Lonergan. “There was also the question of two people being killed.”
He said MacArthur had spent “a long time in prison” and that the authorities deemed him to be suitable for release on the basis of risk assessment.
“In terms of that, I believe that it is the right thing to do, once people are satisfied. Personally, I have always had a difficulty that, in Ireland, it is still very much a political decision whether somebody is released or not.
“In many other countries it is a judicial responsibility and they put a tariff which is a far fairer system because you can imagine the dilemma... who will have released him first?”
MacArthur has served much longer than the vast majority of killers. As reported in the Irish Examiner last month, the average sentence is 17.5 years.
The Irish Penal Reform Trust yesterday repeated calls for an independent Parole Board to bring impartiality and openness to the process.
“The easy way to improve the system is to set up a fully independent body with the necessary expertise making decisions fully removed from political controversy,” said IPRT director Liam Herrick.
He said the decision should be taken away from the justice minister.
Advocates for Victims of Homicide have called for a review of the law on mandatory life sentences for murder. It wants judges to be given the power to set sentence tariffs — minimum terms before consideration for parole.
Meanwhile, Catherine Nevin could start a pre-release educational course in the coming weeks, for which she would be granted day release.
The “Black Widow” has served 12 years for murdering husband Tom in 1996. It will be June 2013 before the Parole Board assess her for temporary release.
Last night the Department of Justice said while it did not normally comment on individual cases, it needed to make a statement on Nevin “in light of the way this case has been reported”.
It said the justice minister had not made a decision on granting temporary release. “Recommendations have been made concerning attendance on an educational course but no decision has been made.”