The questioning of the 33 suspects in the Noor 1 drug-smuggling case is due to begin on Monday, which will coincide with the end of the 18-month pre-trial detention of four of them.
The trial, which began two months ago, concerns the discovery of 2 tons of heroin in Athens last year.
The drug was shipped to Greece on board the Noor 1 cargo ship. Eleven of those charged were the ship’s crew.
Most of the suspects face charges of drug smuggling and forming a criminal organization. The drugs were found in a warehouse in Koropi, east of Athens, and at a villa in the northern suburb of Filothei.
The four suspects who are due to be released from custody on Monday are Turks. They will have to remain under house arrest and attend the trial after being released.