Bristol crown court heard that Coughlan ambushed Collins shortly before 6pm as he returned from campus on his bike. The attack was captured on CCTV installed at the house, which Coughlan later showed to police, who initially treated him as a witness.
After the stabbing, Coughlan allegedly cycled away on Collins's bike, dumped it at a nearby retail park, bought a change of clothes and threw his bloodstained clothing into a pond. He returned to the house at about 9pm, put a pizza in the oven and did online gaming with friends, the court was told.
Prosecutor Adam Vaitilingam KC said Coughlan waited about eight hours before calling 999 at around 2am, claiming he had just found his friend's body in the garden. He told police he noticed the back gate was open and went outside to investigate.
Coughlan had injuries to his hands but said he hurt himself falling while climbing trees. As the evidence against him mounted, he went from witness to suspect. He now accepts he killed Collins but denies murder, saying he “lost his self-control”, the court heard.
The two men were final-year robotics students at the University of West England and lived together in a house owned by Coughlan. There had been disagreements about rent but friends were unaware of any significant problem. The trial continues.