Police are offering a £15,000 reward for information leading to the arrest of the killer of BBC worker Tom Brown.
Police have issued an e-fit of the murderer
The Met has also issued an e-fit of the man they think stabbed to death the 27-year-old.
The BBC library assistant was attacked as he walked home in the early hours of Saturday in Southgate High Street, north London.
Police will return to the area at 2200 BST on Friday to carry out further door-to-door inquiries.
They believe Mr Brown left his friend's house at about 0300 BST and was attacked outside Chandos Court on The Green.
Police have ruled out robbery as a motive for the attack, as he still had his wallet and phone with him when his body was discovered.
Det Ch Insp Keith Garnish said: "We are keen to trace the man in the e-fit who was seen in the area at about 3.30am.
"This appears to be a completely unprovoked attack and Tom would have had little chance to defend himself.
Mr Brown was killed the day before his 28th birthday
"He had been enjoying a night out with friends and was yards from his home address when he was brutally stabbed.
"Tom was a popular and hard-working man who had everything to live for.
"We urge anyone with information about this incident to contact us as soon as possible."
He also said police were keen to speak to anyone in the area at the time of the attack, particularly the man who found Mr Brown's body.
They especially want to speak to a man and woman, who were seen sitting on a wall at about 0400 BST, 10 yards from the murder scene.
The suspect in the e-fit is described as white, of slim build with a gaunt looking face, 5ft 7in-5ft 10in with light brown hair, short at the sides and longer at the front.
He was scruffy in appearance and was wearing either a grey or white-hooded tracksuit top.
Mr Brown was murdered the day before his 28th birthday.