Zack Coughlan, a final-year robotics student at the University of the West of England (UWE), initially denied murder but admitted killing Collins. He told jurors he stabbed his housemate because he feared Collins would kill him, citing a dispute over rent and differing political views.
However, after a legal ruling by trial judge Justice Linden that Coughlan's partial defence of manslaughter by reason of loss of control could not be left to the jury, he changed his plea to guilty. The judge discharged the jury, thanking them for their service.
Coughlan had installed CCTV cameras around the property, which captured the entire attack. Police said he later rewatched the footage five times. After the stabbing, he cycled away Collins' bike to dispose of bloodstained evidence, dumping it at a nearby retail park. He bought a change of clothes and threw his bloodstained clothing in a pond, weighed down in carrier bags with bricks.
On returning home, he ate pizza and played video games, telling officers he "had to disconnect" from what happened. He did not call 999 for another five hours. Police bodyworn camera footage showed him feigning shock when officers arrived.
Detective Chief Inspector Lucy Edgeworth of the major crime investigation team described the murder as "meticulously planned" and a "cold-blooded execution". She said inconsistencies in Coughlan's story included claims he had injured his hands climbing a tree after the incident, which she called "slightly odd". His DNA was found on bloodstained clothing recovered from the pond.
In a statement, Collins' family said his death had affected them in a "deep, profound and lasting way". They added: "Our family has been sickened that Zack Coughlan pretended to help Jamie when in fact he is responsible for killing him." Collins, from Swansea, was posthumously awarded a 2:1 degree in July. UWE Bristol vice chancellor Steve West described him as a "natural engineer" and "a valued member" of the robotics community.
Coughlan will be sentenced for murder on Wednesday.