The parents of Siobhan Phillips, who was left for dead when her partner opened fire on her and Garda Tony Golden, are requesting an investigation "at the highest level" on behalf of their daughter into developments reported on in last night's RTE Primetime programme.

Heroic Garda Golden was killed by Adrian Crevan Mackin in October 2015, before Crevan Mackin turned the gun on himself.

A documentary broadcast by RTÉ has raised questions about why shooter Crevan Mackin was not convicted on weapons charges after he admitted to weapons possessions during an interrogation.

His family have claimed he was an informer and have questioned why he was freed on bail after he was arrested for buying weapons online.

The programme also carried claims Mackin was sent to Portlaoise Prison to “spy” on the Real IRA and was later released on reduced bail after republicans refused him access to their wing.

His sister said that in the aftermath of being imprisoned he became paranoid and violent toward his partner.

Reacting to last night’s programme, the family said in a statement today:

"This is a significant development in relation the family’s pursuit for information and accountability relating to the serious shooting of Siobhan on 11th October 2015 and the serious threat to the family beforehand.

"These revelations raise issues of significant public importance and require an investigation at the highest level.

"We have been instructed today to issue proceedings in the High Court in Dublin and we will be writing to Frances Fitzgerald, the Minister for Justice, requesting that she immediately establish a public inquiry into the circumstances surrounding the shooting of Siobhan and the murder of Garda Golden."

Siobhan's father, Sean attended Omeath garda station in Co Louth on the Sunday of the shooting with his daughter and other family members.

The family had made an appointment with gardai in order for Siobhan to make a statement about a sustained attack which Crevan Mackin had inflicted on her.

During a 12-hour attack Crevan Mackin beat Siobhan, cutting her on her arms and legs and making threats against her and her family.

After the statement had been made Siobhan, Gda Golden and her dad made their way to the home she had shared with Crevan Mackin.

“It happened that quick, inside about two minutes," Mr Phillips said.

"He said 'what are you doing here?' Then Tony Golden said 'Siobhan is here to collect her things'. He didn’t answer Tony.

"Then I heard bang, bang, bang, bang, bang, bang. I was running, zig zagging... I was actually shouting the names of my kids [thinking that I would be killed],” he said, growing emotional as he recalled the ordeal.

Fianna Fáil’s Justice and Equality Spokesperson, Jim O’Callaghan, also reacted to the programme, saying; "Last night’s Primetime documentary about the murder of Garda Tony Golden and the maiming of Siobhan Phillips raises issues of considerable concern.

"The documentary revealed that at the time of Garda Golden's murder, Gardaí were aware that Crevan Mackin had admitted in interviews to the importation of bomb making materials and parts for 6 firearms.

"He had also admitted responsibility for the possession of 2 guns in an unused property near his home.

"This information had initially been brought to the attention of the Gardaí by the Federal Bureau of Investigation.

"Notwithstanding these admissions, Mackin was not charged with possession of this serious arsenal. Instead, he was charged with an offence he did not admit to and which therefore would have been more difficult to prove, namely membership of the IRA.

"What is even more disturbing is that after Mackin was excluded from the Republican wing in Portlaoise prison, a term of granting him bail was significantly reduced. This had the effect of permitting this dangerous man, who was self-medicating for anxiety, back into the community.

"Garda Golden should have been made aware prior to accompanying Siobhan Phillips to Mackin’s home in Omeath that this was a dangerous man who had admitted to the importation and possession of guns. Had Garda Golden been aware of these factors he most probably would not have approached the premises without armed support," he continued.

"If Mackin was a Garda informant, as was suggested by the programme, and was prosecuted with an offence that would facilitate his informing, rather than the serious offences to which he admitted, then this needs to be explained by the relevant authorities.

"Garda operational matters are not the concern of politicians but if decisions are made by State authorities that expose the community to danger, then those decisions must be explained and subject to scrutiny.

"There is no more serious offence than the murder of a member of An Garda Siochana; it is an attack upon the whole community. The bravery and memory of Garda Golden, and the horrendous crime committed against Siobhan Phillips require that a full explanation of the State’s involvement in the matters identified in the programme be provided."