A verdict of unlawful killing has been returned at the inquest into the death of Garda Tony Golden.
The officer, who was based in Dundalk Garda Station, was shot five times by Adrian Crevan Mackin at a house in the village of Omeath, Co Louth on October 2015.
He had been helping Mackin's partner Siobhán Phillips collect her belongings from their home following an alleged domestic assault.
Mackin (24), who had previously lived at several addresses in Newry, shot Garda Golden and Ms Phillips before killing himself.
The fatal shot was fired into Garda Golden's back, the inquest in Dundalk heard.
Ms Phillips, the mother of Mackin's children, was left blinded in one eye.
At the time Mackin had been facing a charge of IRA membership and was on bail.
In her evidence, Ms Phillips said he had subjected her to a prolonged assault from 5pm until 7am two nights before the attack on Garda Golden.
She said Mackin was quiet when she returned from work and was contacting another girl, who told him she would not talk to him any more because he was a paedophile.
Mackin blamed Ms Phillips' family for the claim.
During that evening and night, he punched his partner, cut her with a knife, kneed her in the ribs, and tried to strangle her.
She said the next morning, he told her to put on make-up and go to work.
She later contacted her father and stepmother and attended the Garda station, where she was advised to seek medical attention.
Ms Phillips' father Sean Phillips told the coroner's court he had been "agitated" that a statement had not been taken.
He said when he contacted Garda Golden the next day, the officer took a statement from Ms Phillips and suggested going to the house with her to collect clothes.
Mr Phillips said he stayed in the car while his daughter and Garda Golden went into the house. About one minute later, he heard several bangs.
He told the court he would never have gone to the house if he has known Mackin had a gun.
"Mackin was a monster and we want to know why he was out of jail," he said.
