The Metropolitan Police said in a statement tonight that they urgently need to talk to Shane O'Brien, 27, of Ladbroke Grove, following the death of Josh Hanson, 21, on Sunday, 11 October 2015.
Josh, from Kingsbury, died after suffering a serious wound to his neck and the murder investigation has gained nationwide coverage, having been featured on the BBC Crimewatch show late last year.
So far two men have been arrested as part of the investigation.
The Metropolitan Police statement read: “Officers continue to appeal for information on the whereabouts of man they wish to speak to in connection with the murder of Josh Hanson in Eastcote last year.
“A £10,000 reward is available for information leading to O'Brien's arrest and prosecution. Officers say although he has links to the Ruislip area he could be anywhere in the country.
“Shane (pictured below) is described as a white man, 6ft tall and of muscular build. He should not be approached by members of the public. Any sightings of him should be reported to police immediately on 999.”
Detective Chief Inspector Noel McHugh, who is leading the investigation for the Homicide and Major Crime Command, said: "We are very keen to speak to Shane O'Brien as part of our ongoing enquiries and we believe he could be anywhere in the UK.
"I would appeal directly to O'Brien to contact us, or ask that anyone who has seen him or who knows where he is to contact us as well. I do believe someone out there will know where he is.
"A substantial reward remains on offer to anyone with information that leads to O'Brien's arrest and prosecution and we hope this will encourage someone to come forward.”
The Met statement added: “On Wednesday, 28 October 2015, detectives arrested a 24-year-old man and a 29-year-old man - who were on an inbound flight to the UK - on suspicion of perverting the course of justice and assisting an offender.
“Both were taken to a London police station and bailed pending further enquiries and are next due to return on a date in late March.
“Anyone with information about the murder or O’Brien’s whereabouts are urged to call the incident room on 020 8785 8099 or contact Crimestoppers anonymously on 0800 555 111 or via crimestoppers-uk.org.”
More than £21,000 worth of donations flooded in in just three days for a fund dedicated to Josh.
The campaign page read: “Not only was Josh a hardworking man usually working 7 days a week he was loving, caring and funny.
“He was an angel with a big heart helping and supporting his family and friends was something he did naturally without a seconds thought. He had just left the hospital with his girlfriend after visiting her father and was on his way to meet family and friends.
“Josh has left behind a mother and sister who he supported and would be rallying around for anyone else in this tragic situation.”
DCI McHugh said: "Josh was a hard-working young lad, up at 5am for his job as a roads planner and often working seven days a week. He had everything to live for and when he went out that Saturday night, no one could have imagined what would happen to him.”