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I'm struggling to see what he was arrested for. Is he being accused of money laundering purely because he ran an exchange? There is no applicable law that exists in Greece or Russia that would justify his arrest, based on the information given in the article.
If this relates to a specific instance of "laundering" such as bitcoin received from ransomware victims, surely he can't be held accountable for that. Also, saying he didn't cooperate and using it as an excuse to arrest him is bullshit too, because all of the information regarding transactions to different wallets is public already, they wouldn't need him to release it. Something has been going on behind the scenes now for the past couple of months, this isn't an isolated incident.