Garda Golden was shot in Louth in October 2015 by Adrian Crevan Mackin
There are calls for a public inquiry into all the circumstances surrounding the death of Garda Tony Golden two years ago.
Garda Golden was in uniform and unarmed when he was shot dead by Adrian Crevin-Mackin - a man with previous convictions for possession of firearms.
In October 2015, Siobhan Phillips made a complaint of domestic violence against her partner Mr Mackin.
Garda Tony Golden accompanied her to the home she shared with the 25-year-old at Omeath in Co Louth.
When they went in, Mr Mackin shot Siobhan and Garda Golden a number of times.
Siobhan was critically injured but survived. Garda Golden, a married father of three, died from his injuries.
In light of information that came to light last year, GSOC has opened an investigation into the circumstances that led to what happened that day.
Among the watchdog's line of inquiries is the extent and nature of interaction between gardaí and Mr Mackin, who was on bail at the time.
Ms Phillips and her family are also due to initiate High Court proceedings and have called for a public inquiry to investigate matters - including what they describe as the "serious threat to their family beforehand".
The Taoiseach is being urged to recall the Dáil after the new information emerged in a Prime Time Investigates programme, which alleged gardaí had a litany of information about Mr Mackin and the weapons he had.
Ms Phillips' father, Sean, told LMFM Radio why he wants a number of face-to-face meetings.
"There is absolutely no accoutability and to be honest, I would have no faith in a GSOC investigation, considering we only received the letter from GSOC less than 12 hours after RTÉ went to the guards with a list of questions.
"Really what I'm looking (for) is a public inquiry or an inquiry carried out by a force that isn't the guards or the PSNI".
A statement on behalf of Ms Phillips and her family - from Katie McAllister of Madden & Finucane Solicitors - reads: "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 enquiry into the circumstances surrounding the shooting of Siobhan and the murder of Garda Golden."
In a statement, GSOC says it has been investigating the circumstances leading up to and including the death of Garda Golden, and what it describes as the "apparent self-inflicted death of Adrian Crevan Mackin and the serious wounding of Siobhan Phillips".
The scope of the investigation - which was launched late last year - will focus on:
GSOC said in a statement: "Full and timely cooperation of the Garda Síochána and other organisations will be critical to the effectiveness and progress of this important investigation. The Garda Síochána Ombudsman Commission will use all its legal powers to try to ensure this cooperation."
Sinn Féin leader Gerry Adams said: "All of the families affected by this need to have truth about the circumstances of Crevan Mackin’s arrest, questioning, charging and relationship with An Garda Síochána.
"Those responsible must be held accountable and, if necessary, they must face a criminal investigation and possibly charges. The Taoiseach must now recall the Dáil for next week so that the Minister for Justice can make a full statement and take questions on this very serious matter."
Sinn Féin deputy leader Mary Lou McDonald added: "It raises the most serious of questions. I think anybody watching that programme would have been deeply shocked.
"There is no doubt now that there are very, very serious questions again for the Garda Commissioner, against for the Minister for Justice, and again for An Taoiseach."
Fianna Fáil’s justice spokesperson Jim O’Callaghan, meanwhile, argued: “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.”