Published Wednesday, 01 February 2012
The man, known only as witness M, gave evidence via video link at Belfast Crown Court on Wednesday.
He said he was walking in Craigavon with his family and dog when he saw Brendan McConville at an electricity box.
The prosecution claim that is where the gunman stood to fire the fatal shots, during the attack on 9 March 2009.
Witness M told the prosecuting QC he had known McConville since the former Sinn Féin councillor was a child and that he saw him twice that night - once on the way to his destination and again on the way back.
He told the lawyer he first allegedly saw him shortly after 7pm standing with four other men and then again on the way back, sometime between 9pm and 9.30pm, this time standing with two other men.
Describing how McConville was wearing a green army jacket, he claimed McConville said "hello" to him and that he "nodded hello" back but that he was anxious to get away as he could see another man standing on top of a hill nearby.
Witness M said he reported the incident to police in February 2010, after a man whom he knows and has labelled "person A" came to his front door told him to "keep your gob shut".
"At the start I thought it was a joke but then I realised that it was something to do with the police officer being shot," claimed witness M.
During cross-examination by the defence QC, witness M was asked if he was considered a Walter Mitty character?
On occasion the lawyer inquired, "Do you tell tales or fibs, make up stories that aren't quite true?"
"No," he said.
Witness M also denied having alcohol and eyesight problems.
Constable Carroll, a 48-year-old married man and grandfather with 24 years' service in the police, was nearing the end of his 12-hour shift when he was sent to a 999 call-out in Lismore Manor, Craigavon where a gunman was lying in wait 50 metres away.
He was killed just two days after Sappers Mark Quinsey and Patrick Azimkar were murdered at Massereene army barracks in Antrim.
McConville, 40, from Glenholme Avenue in Craigavon stands accused of the murder alongside 20-year-old John Paul Wootton of Collindale in Lurgan.
The pair deny the charges against them.
Wootton's mother Sharon Wootton, also from Collindale, Lurgan, faces a charge of perverting the course of justice on dates between 8 March 2009 and 20 October 2009 in that she allegedly gave false information to police and "removed a computer or computers from her home address believing her home address might be searched and the said computer or computers seized by police".