The trial has begun in Tenerife of an Englishman accused of killing a young Irish tourist on the holiday island over 16 years ago.
Darren Sapstead, from Essex, is accused of causing the death of Garry Walton, who lived near Waterford, during a "booze cruise" in Playa de Las Américas on 7 November 1996.
Initially believed to have been an accident, a Spanish court later ordered the investigation to be reopened after one of the passengers changed her version of events.
The passenger told police that Mr Walton, who had been drinking heavily on the cruise, had been deliberately pushed into the water by the defendant.
According to Spanish state prosecutor Deborah Padilla, Mr Sapstead, now 38, "grabbed Mr Walton without warning by the legs and threw him over the side of the boat into the water".
His body was recovered from the sea several hours later.
The prosecution's case centres almost entirely on the evidence of two sisters, Katie and Lucy Smethurst, who were among the approximately 40 young holidaymakers on the boat trip, many of them Irish.
Both have been called as witnesses and are due to testify tomorrow.
Mr Sapstead denies the charge and fought a nine-year battle to avoid extradition to Spain, taking his case to the High Court in London.
The court was told today that Katie Smethurst, from Manchester, initially denied any knowledge of the incident but later made a statement to British police implicating Mr Sapstead.
According to the prosecution, she described how "an extremely drunk Garry Walton" approached her and Mr Sapstead on deck, with the latter allegedly saying "Shall I throw him overboard?" before pushing him over the handrail seconds later.
Her sister Lucy allegedly told police that at a meeting the following day at the sisters' resort hotel, they were urged by Mr Sapstead "to keep quiet" about the incident.
Addressing the court, Mr Sapstead said he "had no involvement whatsoever" in Mr Walton's death and had only realised someone had fallen overboard when he heard the commotion in another part of the boat.
"No-one, not even the crew, was doing anything. I started taking my shoes and T-shirt off to jump in but I was told by a crew member that it was too dangerous. I grabbed a lifebelt and threw it into the water, but by that time the boat had travelled some distance" he said under cross-examination.
Asked by defence lawyer Carlos Valenciano if he could think of any reason why Ms Smethurst should implicate him over one year after the incident, Mr Sapstead said he was "hoping to find out tomorrow when she appears in court".
The trial before a jury in the Tenerife capital, Santa Cruz is expected to last until Thursday.
Mr Sapstead faces 12 years in a Spanish jail if found guilty.
Mr Walton's parents, Robert and Catherine, have flown to Tenerife for the trial, having learnt only late last week that it was taking place.
"We had no idea this was going to happen. We don't expect very much but we had to come for Garry's sake" said Robert Walton outside the courtroom this morning.