Patryk Makuch, 37, mingles with unsuspected travellers heading to Europe, just 12 hours after allegedly stabbing Kamil Malysz to death in west London.
Detectives appealed for public help to find Polish national Makuch who is wanted under a European Arrest Warrant.
A £20,000 reward is offered for information leading to his capture. Makuch could be in his native Poland or anywhere in northern Europe.
The family of Mr Malysz, 34, are distraught nobody has faced justice three years after the brutal killing.
He was found in a shared house in Alfred Road, Acton at 10.15am on January 27, 2019.
Police attended the address after concerns were raised for Mr Malysz’s welfare.
The Polish national was pronounced dead at the scene and a post-mortem examination found the cause of death to be haemorrhaging due to a stab wound.
Detective Chief Inspector Katherine Goodwin, of the Met’s Specialist Crime Command, said: “Today we have released footage of Makuch boarding a Eurostar train at St Pancras International station on 28 January 2019 just 12 hours after Kamil was attacked. He has been on the run ever since.
“As Kamil’s family continue to live with their loss, Patryk Makuch remains free which only adds to the family’s anguish.
“We have worked hard to trace Makuch’s steps, but despite the considerable efforts made, he has never been located.
“Kamil was just 34 when he was fatally stabbed at a flat in Alfred Road, Acton.
“His life was brutally taken from him and we are as determined as ever to find Makuch and place him before the courts.
“I urge anyone who knows where this dangerous man is to do the right thing and call the Met incident room or contact the local police force in Europe.”
Under the European Arrest Warrant, anyone visiting or living in Europe can contact local police with information about Makuch’s whereabouts and could be eligible for the reward if their tip leads to his arrest.
Anyone with any information is asked to call the Operation Racine incident room on 020 8785 8244 or Crimestoppers anonymously on 0800 555 111.