Mr Marshall arrived at a police station with stab wounds
A man has been warned he faces a "long" prison sentence after being convicted of stabbing a 19-year-old to death.
Kandeepan Balasubrahaniam, 22, from Acton, west London, killed Craig Marshall in September last year.
He said that he had not meant to stab Mr Marshall and claimed he was acting in self-defence during a struggle, the Old Bailey heard.
Balasubrahaniam was cleared of murder but found guilty of manslaughter. He will be sentenced in July.
The court was told that the stabbing took place after Mr Marshall complained about the quality of cannabis he bought from Balasubrahaniam.
Mr Marshall died in hospital after arriving injured at Acton police station on 25 September 2008.