A court in Hawaii court ordered the release of Dean Jay Fletcher who is alleged to have killed his Canadian wife in Vava'u.
Mr Fletcher fled Tongan authorities to American Samoa where he was arrested last October by US federal agents.
Tonga sought extradition but the US Secretary of State denied the request.
The US was worried that without a legal aid system, Mr Fletcher would not have legal representation or a fair trial.
But Tonga's acting Attorney General, 'Aminiasi Kefu, said the defendant had already hired lawyers before he fled.
