A man has been arrested in connection with the murder of Richard Whelan, who was stabbed to death on the top deck of a London bus.
The attacker had been harassing Mr Whelan's girlfriend
Scotland Yard said the 20-year-old was arrested in Walton-on-Thames in Surrey on Friday and is being questioned at an east London police station.
Mr Whelan, 28, was stabbed up to six times by a man on the number 43 bus in Islington, north London, a week ago.
Police said the attacker had been harassing Mr Whelan's girlfriend.
Mr Whelan, from Kentish Town, north London, and his girlfriend got on the bus at about 2145 BST.
The attacker got on at the same stop and all three of them went up to the top deck.
The man started throwing chips and shouting at other passengers until most of them went downstairs.
Police said when he turned his attentions to Mr Whelan's partner, who has not been named, the victim intervened.
He was then stabbed up to six times, despite the efforts of his girlfriend to pull the attacker off him.
Mr Whelan chased the man to the lower deck but collapsed. He died an hour later, from a stab wound to the heart.
The attacker was seen to walk away from the bus in Holloway Road near the junction with Wedmore Street.
Police have said there are still people on the bus at the time who have not come forward.
Upper deck passengers on another 43 bus, which was following behind, are also urged to come forward.