Jack Robinson, 18, of no fixed address, denies murdering 53-year-old Raymond Boyle, while Daniel Mynott, also, 18, of Haviland Way, Kings Hedges, who appeared next to Robinson in the dock, denies the charge of grievous bodily harm with intent. David Matthew for the prosecution told the court on the first day of a trial expected to last more than two weeks Mr Boyle was punched, stabbed, and had his head stamped on in the early hours of June 22, last year. Mr Matthew told the court: Both defendants who were interviewed said the attack broke off when one of them would walk away, then one of them would come back again and start again. This was no quick attack. This was a drawn-out beating of a man who was essentially helpless. Jack Robinson has admitted being involved in the attack. He has admitted kicking him and stamping on Mr Boyles head. He came across as far the more aggressive of the two. Mr Matthew said Mynott and Robinson, who were friends, had left Mynotts house on the evening on June 21 before buying beer at a shop in Milton Road and walking into town. He said once they reached the city centre they stopped to drink the beer on a bench on Jesus Green next to the River Cam and that is where they met Mr Boyle - who had been wandering around Cambridge more than four times over the legal drink drive alcohol limit. Mr Matthew told the court Robinson had asked Mr Boyle for a cigarette which he then complained smelled odd. The prosecution said Robinson then without warning, punched Mr Boyle in the face and hit him again and knocked him down. In his opening statement, Mr Matthew said witnesses had told the police Robinson had been shouting Dont mess with us. He said the same witnesses would tell the jury later in the trial they saw one of the attackers try to stop the other from carrying on. He continued: Two teenagers who were fishing on the other side of the river saw that Mr Boyle had two attackers and both of these two saw that both of the attackers kicked Mr Boyle on the ground. One of [the teenagers], then saw one of the attackers try to push the other one away - that was clearly Daniel Mynott who came to his senses and tried to stop his friend. The jury was shown CCTV footage of Mr Boyle at Jesus Green bridge an hour before he was found dead. Mr Matthew was not able to finish his opening statement and it will continue tomorrow morning - but he said a pathologist will tell the court Mr Boyle died of blunt trauma to the head and chest before immersion in water. Mr Boyle was immersed in the water while still alive but possibly incapacitated, Mr Matthew said. The case continues.