A witness to the murder of a bus passenger who was stabbed by a man who had been throwing chips at people, is being urgently sought by police.
Mr Whelan tried to stop his attacker from escaping despite his injuries
The man was the only other person on the top deck of the number 43 bus when Richard Whelan, of Kentish Town, north London, was attacked on Friday night.
The 28-year-old was stabbed up to six times when he tried to stop the knifeman harassing his partner.
The attacker was said to walked off down Holloway Road after the attack.
Police said Mr Whelan, a hospitality agent who sold tickets for sporting events, endured the man throwing food and shouting at passengers for about 15 minutes.
His behaviour had caused all but the remaining man to move back down onto the lower deck.
When the man then started to abuse Mr Whelan's girlfriend he defended her.
Police said he was then stabbed up to six times as his girlfriend tried to pull the attacker off.
She is said to be deeply traumatised by the attack.
Despite his injuries, Mr Whelan then attempted to stop the man getting away, before collapsing on the bottom deck of the bus.
Mr Whelan's attacker is described as black, in his 20s, just under 6ft tall with afro hair and wore a dark jacket and a hooded top with the hood up.
Police said he got off the bus at Holloway Road near the junction with Wedmore Street.
Det Ch Insp John Macdonald said: "I have reviewed the initial evidence and Mr Whelan did absolutely nothing wrong whatsoever.
"This was a totally unprovoked attack by someone who obviously carries a knife as a matter of course."
On Monday, it emerged Mr Whelan had helped to console the family of a close friend who died in the 7 July bombings.
Ciaran Cassidy, 22, died after an explosion on a Piccadilly Line train near King's Cross station.
His mother Veronica described Mr Whelan's murder as tragic.