The mystery man claimed Irishman Eric Wilson, aged 27, pulled down the visor of his crash helmet as he rushed up to British expat Dan Smith, aged 24, on a packed Spanish bar terrace and shot him eight times.
Wilson, from Ballyfermot, Dublin, is standing trial for murdering roofer Mr Smith on June 5 last year at the Lounge Bar in Riviera del Sol near the resort of Fuengirola after an earlier argument over a girl.
The witness, speaking from a neighbouring room with his voice distorted by a machine, alleged in a Malaga court that he saw Wilson’s black Yamaha R1 motorbike being driven slowly past the bar at 10pm.
He said: “I didn’t see the argument Eric and Dan had earlier but I was told about it.
“When Daniel saw the motorbike he told everyone on the terrace to get inside the bar. He did it because the man on the bike was looking for problems.
“Dan stayed on the terrace. The killer had the visor on his helmet up as he appeared on foot a few moments later from a side street.
“I could see his face and I saw it was Eric. He shouted as he approached Dan and put the visor down.
“He had a pistol in his hand and shot Dan. Dan fell to the floor. I heard eight shots, fired in quick succession.
“Dan wasn’t able to defend himself.”
Wilson was ushered to the witness stand so he could not see the witness, an acquaintance of the alleged killer and victim.
Quizzed by Mr Smith’s family lawyer Carlos Comitre, the witness, who had to be persuaded by the judge to take off a crash helmet while testifying, told the jury: “The first shots Eric fired were from about 12 metres away and they got closer as he approached Dan. The last were all from close range.”
Bar owner Steve Reynolds told the court Wilson and Mr Smith had argued earlier that day.
Forensic expert Fernando Martin Cazorla told the court he concluded the victim was shot eight times, including twice in the testicles as he lay on the ground.
One bullet knocked out several teeth, which were found by his body.
The killer bullet pierced a lung and caused severe respiratory failure.
Five bullets were removed from Mr Smith’s body during an eight-hour autopsy.