Piotr Kupiec, 28, was wanted by Polish authorities over the death of a man following a football match in 2007 was put on Interpol's most-wanted list.
He was arrested in Wiltshire in January at a Subway restaurant where he worked - just 500 yards from a police station - and was due to appear at Westminster Magistrates Court on Wednesday for an extradition hearing.
But the European arrest warrant under which he was detained was withdrawn on Tuesday because police investigating the case arrested another man with the same name, making it invalid.
Freed: An admin bungle meant a judge had to release Kupiec for him to be rearrested Most wanted: Kupiec on the Interpol site Read more: Top cop believes John "Goldfinger" Palmer was killed by professional hitman
A new warrant was due to be issued at the London court and Kupiec rearrested, but an administrative error meant he was not brought there on Wednesday from Wandsworth Prison.
District Judge Quentin Purdy said there no lawful reason for him to be held and ordered him to be freed.
Kupiec was formally released from prison but detained under a fresh European arrest warrant moments later.
Scotland Yard said he was taken into custody at a London police station and would appear at Westminster Magistrates Court on Thursday.
