But how would that happen and who would take on that job?
The first thing to understand is what a commission of investigation does and how it works.
“A Commission of Investigation is a fact-finding mission, no more than that,” says Prof Shane Kilcommins, head of School of Law at the University of Limerick.
“They are set up to be quick and can compel information and people to appear before it. It can draw a broad picture.”
Dr Seán Ó Conaill, lecturer in constitutional law at University College Cork, agrees: “The Charleton report will be based on the terms of reference. It works on a fact-finding basis — the what, where and why. It can’t make determinations.”
Prof Kilcommins said the threshold of proof in a commission of investigation is on the balance of probabilities.
“This is the burden of proof that exists in civil proceedings. It is significantly lower than the burden of proof required in criminal proceedings, which is expressed as ‘beyond reasonable doubt’ standard.”
In addition, Prof Kilcommins said that evidence given to commissions is “not admissible” in other proceedings (save in limited circumstances).
That means any body tasked with a criminal investigation has to start from scratch. But the report can act as a useful guide.
“The report would be a useful roadmap,” said Dr Ó Conaill. “Any possible criminal offence flagged will be by-the-by. It could say ‘this was discovered during our investigation and warrants further investigation’.”
Commissions of investigations, in general, are held in private, though the commission can decide to hold certain evidence in public.
Yesterday, Sgt Maurice McCabe said he was opposed to a private inquiry and called for a public inquiry, citing his experience with the O’Higgins commission.
But like commissions of investigations, tribunals of inquiry are also fact-finding and are similarly constrained against making judgments on the rights of individuals.
Dr Ó Conaill pointed out that previous tribunals had made determinations on individuals and subsequently had to withdraw them on foot of court orders.
If Mr Justice Charleton considers that some matters require further investigation he might send his report to the DPP or the Garda Síochána Ombudsman Commission (Gsoc), as well as to the justice minister.
It is highly unlikely the Minister or the DPP will refer it back to the Garda commissioner for investigation.
Sgt McCabe has previously indicated a preference for an external criminal probe — and he has been backed in this call by Labour leader Brendan Howlin, who urged a “fresh approach” rather than another commission.
“I can’t see how it would be possible,” said Prof Kilcommins. “I’ve never heard of an international body coming in here to investigate. It would have no jurisdiction here.”
To both academics, Gsoc is the only body capable of conducting such an investigation.
“Gsoc is the obvious and most appropriate body,” said Dr Ó Conaill. “They know how to do it.”
Prof Kilcommins said: “Gsoc, for me, are the only ones. They are independent of the Garda Síochána and can initiate investigations.”
And Gsoc have been here before.
Currently, they are investigating matters arising out of the O’Higgins report into the treatment of Sgt McCabe. That investigation was referred to it by Ms Fitzgerald.
Back in 2013, Gsoc launched a public interest investigation following the publication of the Cloyne Commission report in 2011. That commission indicated gardaí did not act on information received in relation to complaints of sexual abuse in the diocese. The Gsoc report, published in 2015, did find evidence of Garda failures but not evidence of offences having been committed.
So, if the Charleton report flags possible criminal behaviour on the part of gardaí, how could a subsequent investigation be launched? Like with the O’Higgins inquiry, it could start with a request from the justice minister under Section 102 (5) of the Garda Síochána Act.
Gsoc does not need to have any such a request and can, off its own bat, launch an investigation, including a criminal investigation.
Following recent amendments, Gsoc can now investigate the Garda commissioner — but crucially requires the consent of the justice minister.
Gsoc has had long running battles regarding getting documentation from An Garda Síochána — something which the chair Ms Justice Mary Laffoy raised at the Oireachtas justice committee.
She called for statutory powers to get such documents and recourse to court orders if such requests are ignored.
Ms Fitzgerald indicated to the Dáil last month she was drafting laws to give is such powers.
But, if Gsoc launches a criminal investigation, it has all these powers.