Garda killer Aaron Brady attacked a key witness and warned him to "keep his mouth shut" after he was overheard bragging about the Adrian Donohoe murder.
The assault was just one of several attempts by Brady to prevent people in the US from giving incriminating statements against him to detectives.
Two people testified during the trial that they heard the Crossmaglen man admit to shooting a guard, but five more people made statements linking him to the murder.
The Herald can reveal that one of these men was attacked by Aaron Brady after overhearing him making a drunken bar admission.
The witness told detectives that he was in the Coachman's Inn pub in the Bronx on St Patrick's Day 2015 when he overheard a man tell his friends what it was like to kill someone.
Gardaí were told that the man was boasting about the murder and that he later assaulted the witness outside the pub, warning him to keep his mouth shut.
The witness said he later identified his attacker as Aaron Brady after seeing him in a Crossmaglen Rangers jersey on a friend's Facebook page.
The man, from Northern Ireland, was tracked down by detectives in December 2017 with the help of Homeland Security Investigations (HSI).
Detectives took a detailed statement, which was described as "highly significant", from him.
They also photographed the scar that the witness said was left above his eye after Brady assaulted him.
However, the Northern Irish man, who is wanted by the PSNI in relation to other criminal matters, refused to come to court and expressed concerns about giving evidence.
The man was just one of 68 people who were tracked down by US agents attached to the HSI as part of their efforts to help gardaí.
The pub where the witness said the alleged confession happened was the same bar where he made other drunken admissions.
Barman Daniel Cahill, originally from Dublin, told the murder trial that he twice overheard Aaron Brady admit to shooting a guard in Ireland while he was drinking in the Coachman's Inn on Katonah Avenue.
On one occasion Brady threatened he would shoot a man who punched him in a bar fight and that he had killed before, and on a separate night he was drunk and upset when he admitted the killing.
Brady also claimed during the trial that he was attacked by Daniel Cahill on St Patrick's Day 2015 - which was vehemently denied by Mr Cahill.
This was the same night that he is alleged to have bragged about the killing before attacking the other witness.
One source said: "It was just another example of Brady's mouth getting him into trouble and trying to intimidate those who could link him to Adrian Donohoe's murder."