An expert witness told a jury at Dublin Circuit Criminal Court that Garda Paul Daly hit a protester with his baton at the junction of Parliament Street and Dame Street during the "Reclaim the Streets" demonstration on May Day 2002.
Mr Andrew Laws, a consultant forensic imagery analyst, was giving evidence in the trial of Garda Daly and Garda Fergus Hogan, both attached to Pearse Street station. They have pleaded not guilty to assault causing harm to Mr Emmet Bunting (28), Collins Avenue, Dublin, on May 6th, 2002.
Mr Laws told Mr Tom O'Connell, prosecuting, that he concluded after analysing video footage of the assault on Mr Bunting that "man A punches the protester and he falls to the ground".
Then Garda Daly strikes the protester twice in the lower region of the torso with his baton.
He had been asked by the prosecution to compare an image of Garda Hogan taken on Burgh Quay to the man suspected of punching the protester (known as man A).
Mr Laws told Mr O'Connell he was unable to find differences between the two men significant enough to conclude that they were not the same man. He did find significant similarities between the two and made reference to the shape of the ear and nose, and similarities in clothing and jewellery.
"Based on the facial features, in my view there is strong support to contend that the two men [the man identified as Garda Hogan and the man who punched Mr Bunting] are one and the same."
Mr Laws agreed with Mr Gerard Clarke, defending, that he had no formal training in facial imagery but added that no such training was available.
He agreed that he initially thought Garda Daly hit Mr Bunting on the head with his baton, but after viewing the assault from a different angle concluded that he was in fact hit on the torso.
Mr Laws said it was not possible to see the actual contact of the man's fist with Mr Bunting's face, but in his view it was "a good old-fashioned punch. The video speaks for itself."
He did not accept a suggestion from Mr Clarke that it was possible that as the punch was thrown the protester moved to avoid it and then fell backward.
"It looks like a punch and has all the characteristics of impact being made, but I agree that you cannot see the contact."
Mr Ashley Windsor, an expert in imagery and facial analysis, told Mr Clarke he believed the methods used by Mr Laws were not accurate.
He said there was little evidence of similarity between Garda Hogan and man A, bar the fact they were two uniformed gardaí, with white skin and dark hair.
He found discrepancies in the hats of both men, the rear part of the skull, their nasal profile and their chin profile.
Mr Windsor looked at the video footage and selected a number of uniformed officers whom he found to have similar basic profiles to that of Garda Hogan and concluded that he could not agree with the prosecution witness that the two men were the same person.
Mr Windsor told the jury that, in the period just after the alleged punch on the injured party, an officer in a blue uniform seems to strike the head of Mr Bunting as he falls to the ground.
Mr Windsor agreed with Mr O'Connell in cross-examination, that the footage appeared to show a garda wearing a cap lunge forward and strike out at Mr Bunting, knocking him backwards.
He said the footage did not show the point of contact and the protester's head moves in the opposite direction to which it should have, if the garda's fist had made impact with his face.
He did not accept a suggestion by Mr O'Connell that although the video did not show the actual impact of the punch, it was obvious that the garda punched Mr Bunting, knocking him backwards.
Mr Windsor told Mr Clarke in re-examination that, if the garda's fist had made impact with Mr Bunting's head, it would either have turned sharply to the right or moved backwards in the direction of the punch.
He said there was no apparent rotation of the head, and it actually moved in the opposite direction.
The trial continues before Judge Yvonne Murphy and a jury.