Alongside convicted triple murderer Sokol Hoxha, police are seeking the whereabouts of a number of other fugitives who have yet to serve sentences or even stand trial in their home countries.
Several have recently been arrested and are fighting extradition, often with legal aid.
About 25 extradition cases concerning overseas murders have had hearings at Westminster Magistrates Court this year, with others concerning people convicted or suspected of attempted killings.
Hoxha, 45, has evaded justice for more than 23 years for three murders in two different countries.
Police thought they had finally tracked him down in Birmingham last month, when a man of the same name was arrested and a knife seized during a domestic incident.
But the suspect, who was remanded in custody for two weeks, had to be released after the extradition judge said there was insufficient evidence that he was the murderer.
Hoxha and an accomplice are wanted in Albania for the March 1997 killing of two brothers he shot dead.
He then fled to Belgium with wife Brunilda Dervishi. But five months later he shot her dead in a Brussels cafe.
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He has been on the run ever since, being convicted in his absence of the two murders in Albania in 2000, and then being sentenced to life in his absence in Belgium in 2010.
West Midlands Police believed they had caught him on August 27.
That Sokol Hoxha was brought before Westminster Magistrates, but although he used an Albanian interpreter, he claimed to be Serbian.
He also had identity documents giving a date of birth differing to the killer’s by almost two years.
And neither the Belgian or Albanian authorities could provide DNA or fingerprint evidence. District Judge Paul Goldspring discharged the extradition request saying he could not be satisfied the defendant was the wanted killer.
Last week the Met Police issued appeals for information about two other men wanted over murders in their home countries.
Arunas Kasciukas, 39, is wanted in Lithuania for a murder committed there in October 2018. He has two fingers missing from his left hand and has links to Dagenham, Forest Gate and Ilford, in east London.
The other sought by the Met is Festim Korra, who is wanted in Albania to serve a 22-year jail term for the murder of Hyqmet Pisha, who was shot seven times in 1997.
Korra was able to flee the country before he could be jailed and is thought to have links to east London and could be using a false identity.
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Det Sgt Peter Rance, from the Met’s extradition unit, said: “These men must not be approached. Anyone who recognises any of these men or has information about their whereabouts should call police.”
Alp Mehmet, chairman of Migration Watch UK, said: “These are seriously bad people. EU free movement has a lot to answer for.
“There have been several foreign fugitives wanted in connection with overseas murders arrested here in recent weeks.”
Another fugitive is Grzegorz Sabramowicz, 44, who is wanted in Poland for a gangland execution.
He denies involvement in the killing and the extradition request was discharged earlier this year for technical reasons. He remains living in the Sheffield area.