The murder of a police officer in the Republic of Ireland by a man from Northern Ireland 18 months ago is being investigated by a police watchdog.
Tony Golden, a member of An Garda Síochána (Irish police) was killed in Omeath, County Louth, in 2015 as he tried to help a domestic abuse victim.
He was shot dead by County Down man Adrian Crevan Mackin, who had a string of convictions and was out on bail.
Questions have been raised about how Gardaí responded to the risk he posed.
FBI tip off
The Republic of Ireland's police watchdog - the Garda Síochána Ombudsman Commission (GSOC) - has confirmed it opened an investigation into the force's handling of the case late last year after it received "information and complaints from several sources".
Irish broadcaster, RTÉ, has reported that the US authorities warned Gardaí that Mackin was importing weapons in the months before the murder.
Mackin's sister told RTÉ's Prime Time programme that she believes he was buying decommissioned firearms and selling them to dissident republican paramilitaries.
The 24-year-old gunman, who had previously lived at several addresses in the Newry area, also had a history of domestic violence.
On the day he murdered the police officer - 11 October 2015 - Mackin shot and critically wounded his own partner, Siobhán Phillips, before killing himself at her house in Mullach Alainn, Omeath.
Garda Golden was unarmed when he accompanied Ms Phillips to the house to collect her things, after she made a statement about violent domestic abuse.
Mackin opened fire as they walked in through the door, killing Garda Golden and leaving the mother of his children blind in one eye.
Ms Phillips and her family have now called for a public inquiry into the case.
Before Mackin moved across the border to Omeath, he had been previously convicted in Northern Ireland of gun and ammunition possession and having extreme pornography.
According to RTÉ, Mackin admitted to Gardaí that he bought component parts for guns and bombs over the internet, months before the murder.
It reported that, after a tip off from the FBI, cross-border police searches took place in counties Down and Louth.
Gardaí found bomb components at his home in Omeath and arrested Mackin.
The programme obtained access to transcripts of his Gardaí interviews, during which Mackin admitted buying the weapons, but refused to comment on alleged links to paramilitaries.
Despite his confessions, prosecutors instructed detectives to charge him with IRA membership - which he denied - as opposed to the firearms offences that he had admitted.
Mackin's solicitor at the time, Paul Tiernan, told RTÉ he found it "very strange that someone who had admitted possession of firearms and who had admitted the importation of component parts for firearms should have been treated in this way".
Mr Tiernan added: "In the vast majority of cases, the strongest evidence against people is their own admissions."
It has been alleged that some of the weapons Mackin admitted to importing are still missing.
In a statement, a GSOC spokeswoman said the watchdog will examine Garda interactions with Mackin in the lead up to the shooting, and whether officers "acted appropriately upon their knowledge of [his] access to, or possession of explosives and firearms".
She said this will include investigating whether or not the force took "measures to mitigate the serious risk that this potentially posed to Siobhan Phillips, the general public and members of the Garda Síochána".
Ms Phillips' family have been critical of how Dundalk Garda station handled their initial complaint of domestic violence.
GSOC's statement said it will examine whether the family was "treated properly by all members of An Garda Síochána and their complaints acted upon appropriately".
Garda Golden, who died trying to protect the young mother, was hailed as a hero and given a state funeral.
In a statement on Friday, a solicitor representing Ms Phillips and her family said RTÉ's revelations "raise issues of significant public importance and require an investigation at the highest level".
They have instructed their lawyer to write to Justice Minister Frances Fitzgerald, seeking a public inquiry, and to issue legal proceedings in the High Court in Dublin.
In a statement, a Garda spokesman said the force "is aware that GSOC is undertaking a public interest inquiry into assertions made in relation to the circumstances surrounding the callous and brutal murder of our colleague Garda Tony Golden by Adrian Crevan Mackin.
"As such, we are precluded from comment on such assertions."
GSOC said the "full and timely cooperation of the Garda Síochána and other organisations will be critical" to its investigation.
The watchdog added it "will use all its legal powers to try to ensure this cooperation".