Update 4.45pm: There has been a call for a public inquiry into the circumstances surrounding the murder of Garda Tony Golden and the serious wounding of Siobhan Philips in 2015.
Garda Golden accompanied Ms Phillips to the home she shared with her partner Crevan Mackin on October 11 2015.
He agreed to go with her after she complained of being beaten by him.
He was shot dead by Mackin after entering the house. Ms Philips was also shot but survived the attack.
It’s believed Mackin then turned the gun on himself.
In a statement, GSOC said it is now 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 Síobhan Phillips”.
The scope will focus on whether Gardaí acted appropriately upon their knowledge of the access to, or possession of explosives and firearms by Mr. Mackin, whether Siobhan and her family were treated properly by all Garda members and whether there was a delay in reviewing the circumstances surrounding what happened that day
Siobhan's family now want a full public inquiry.
The Policing Authority has welcomed the announcement by GSOC of its investigation.
Earlier: A new investigation is underway into the circumstances surrounding the murder of Garda Anthony Golden.
He was shot in Omeath in County Louth in October 2015 by Crevan Mackin - who then took his own life.
A Prime Time Investigates program has alleged that Gardaí had a litany of information about Mackin and the weapons and bombs he had in the months prior to his killing of Garda Golden.
Sinn Féin Deputy Leader Mary Lou McDonald says a full review is needed: "There needs to be a criminal investigation into these turn of events that led to the death of Garda Tony Golden.
"And we believe that the Dáil needs to be recalled immediately."