The man accused of the murder of Detective Garda Adrian Donohoe told a New York barman "multiple times" that he had shot a garda in a "robbery gone wrong", a court has heard.
Daniel Cahill (28), originally from Dublin, was giving evidence via video link from a Homeland Security building in the trial of Aaron Brady, who denies capital murder.
The 13-person jury was told of three interactions between the witness and the accused in New York in 2015 and 2016 in which Mr Brady allegedly admitted shooting a garda.
Mr Brady (29) has pleaded not guilty to the capital murder of Adrian Donohoe, who was then a member of An Garda Siochana acting in the course of his duty, at Lordship Credit Union in Bellurgan, Dundalk, Co Louth, on January 25, 2013.
The defendant, of New Road in Crossmaglen, Co Armagh, also denies robbery of around €7,000 in cash and assorted cheques from Pat Bellew at the same location on the same date.
Yesterday, Mr Cahill told the court that he arrived in New York in August 2013 and began working at the Coachman's Inn bar in the Bronx the following December.
He said he was working one night when Mr Brady was involved in a fight during which he received a gash above his eye.
Mr Cahill told the court that Mr Brady was "repeating that he was going to kill [the man who punched him]" and "that he didn't know the things he was capable of".
Mr Cahill also gave evidence that the accused was speaking to him while facing the mirror and told him he had "shot a member of Garda Siochana" in Ireland and that it was "stupid to retaliate or mess with him".
The jury was told of a separate incident later that year when Mr Brady was drunk in the Coachman's Inn and appeared "very upset".
Mr Cahill gave evidence that the accused "mentioned how a robbery gone wrong led to him shooting somebody".
Asked by lead prosecution counsel Brendan Grehan SC if Mr Brady said who he had shot, the witness responded: "A Garda Siochana. He never mentioned the person by name."
Mr Cahill said that Mr Brady did not go into details about the robbery but said the accused "mentioned multiple times he had shot a garda".
On a separate occasion the following year, Mr Cahill said he went to an apartment after work with three men as well as Mr Brady.
Mr Cahill said the men were talking, "trying to outdo each other", and described the conversations "almost as a p***ing competition".
The witness said that "Aaron decided he was the person there with the most experience because he said that he was the only person there who had killed someone".
He said he could not recall Mr Brady giving much detail "other than the fact he had shot a guard".
The court then heard evidence of a separate interaction in the summer of 2016.
Mr Cahill said he was driving home after work one night and passing Beahan's pub in the Bronx, when he was "flagged down" by Mr Brady.
Mr Cahill said the accused told him that newspapers in Ireland had "written articles about him".
He told the court that Mr Brady took out his phone and showed him a screenshot of an article, which included a picture of men at a football match.
Mr Cahill told the court that he remembered the headline saying something about a man on the run for shooting somebody in Ireland living it up in New York.
The cross-examination of Mr Cahill continues before the Central Criminal Court this afternoon.