Tzortzis added that at the time of arrest Petrac had a fake passport with him.
On Friday the Croatian businessman is expected to be transferred to a maximum security prison on the island of Corfu, where an appeals court is located.
Tzortzis said that the case of two Croatian nationals who were arrested with Petrac, and whose identity he would not disclose, was being dealt with separately.
Greek sources in Igoumenitsa, who spoke on condition of anonymity, said that the two men were Stjepan Hucika and Stjepan Juricko.
Petrac, for whom Interpol issued an arrest warrant, had been on the run since the kidnapping of General Vladimir Zagorac's underage son in February last year. A year later the Zagreb County Court found him to be the mastermind of the kidnapping and sentenced him in absence to six years in prison.
Petrac's name has been repeatedly mentioned in the context of a network helping the runaway Croatian general Ante Gotovina, who was indicted for war crimes by the Hague war crimes tribunal in July 2001.
After the EU in March this year refused to launch previously announced accession talks with Croatia, Croatian Prime Minister Ivo Sanader launched an action plan aimed at breaking up the network of Gotovina's helpers.