Thursday's ruling upheld an earlier decision in April by a lower court, which had judged the Maltese extradition request bid vague and irregular.
The island nation had wanted to arrest former bank employee Maria Efimova for allegedly providing false evidence that could lead to another's conviction, making false accusations to authorities and theft.
Efimova, 35, had helped Maltese journalist Daphne Caruana Galizia, who was killed in a targeted car bombing on Oct. 16. Three Maltese men have been ordered to stand trial for her slaying.
Efimova surrendered to police in Athens in March, citing fears for her life. She is now free.
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