Three suspects, including two alleged ringleaders reported to be members of the armed forces, are being held in pretrial detention for leading a cryptocurrency pyramid scheme that police say pulled in about $8 million and recruited at least 10,000 people.
Prosecutors and investigating magistrates finished hearing the 17 arrested suspects after a marathon process.
The other 14 were released under restrictive conditions and cash bail.
The two alleged leaders, who gave testimony Monday before being sent to prison, denied charges of running a criminal organization, fraud and money laundering.
A third suspect, described in the charge sheet as playing a leading role, was jailed earlier.
Police said the group operated since at least 2025, using legitimate-looking companies and an online platform to promise investors their money would double in just 50 days with little or no risk.
Members allegedly kept recruiting new participants in a pyramid structure. Dozens of victims have been identified.
A victim told iefimerida the pitch worked because early investors appeared to withdraw money. "If we hadn't seen withdrawals, we wouldn't have joined," the victim said.
The inquiry, led by the Katerini Crime Investigation Unit, followed months of work.
Raids last week hit Pieria, Larissa, Mytilene, Patras, Ioannina, Piraeus, Komotini, Preveza, Athens and Kavala, and a further nine people are named in the case file.
Police seized 32 mobile phones, 38 portable storage devices, 16 hard drives, 28 computers, 15 tablets, bank and SIM cards, a cash-counting machine, a CCTV recorder and €295,090.
Greek authorities have warned of rising crypto fraud this year, including a March bust of a 12-member ring that allegedly took in more than €14 million.