Croatia blocks extradition of suspect in Hamas murder
Mohamed Zaouari, 49, was killed in a hail of bullets outside his house in Tunisia's second city Sfax in December 2016.
"The Supreme court accepted the appeal of the suspect... and rejected the request for extradition from the Republic of Tunisia," the court said in a statement.
At a hearing on May 8, the lower court said it had established that "legal preconditions" had been met for the extradition of Alen Camdzic, 46, who has been named by local media.
The final decision will be made by the justice minister.
The suspect was arrested in Croatia on March 13 on an international warrant and has been held in custody since, the court in Velika Gorica, near Zagreb, said in a statement.
Camdzic's arrest was announced by Tunisian prosecutors who said they believed that two people with Bosnian passports had carried out the assassination.
The second suspect, Elvir Sarac, was briefly detained in Sarajevo earlier this week but released when a court refused to hand him over to Tunisia, saying there was no extradition deal between the countries.
'Foreign elements'
Camdzic served in the police during Bosnia's 1990s war and became a professional soldier after the conflict, media reports said.
Tunisia earlier confirmed that "foreign elements" had been involved in the killing of a Tunisian-Belgian citizen.
Shortly after his death, Hamas said he was a drone expert who had worked for the "resistance" for a decade for a decade before being killed by "Zionist treachery".
Israel has not responded to accusations it was behind the killing.
Israel has fought several wars with Hamas, which rules the Gaza Strip, and has assassinated several of the Islamist movement's members in the past.
In November 2017, Zaouari's family denounced "silence" on the part of authorities and called on them to provide more details on the investigation into his killing.
Israel was also accused of being behind the assassination last month in Malaysia of Fadi al-Batsh, a Hamas scientist who was said to be a rocket-making expert.
Family and friends of Batsh accused Israel's Mossad spy agency of carrying out the killing in Kuala Lumpur on April 21.