The police learned that the man converted a small amount of the missing NEM coins into another form of cryptocurrency called litecoin through a site on the darknet, which can only be accessed through special anonymity software, the source said Saturday. The man was aware the NEM had been stolen from Coincheck.

About ¥58 billion ($533 million) worth of NEM was stolen on Jan. 26, with more than ¥500 million worth of it likely to have since been converted into bitcoin and other cryptocurrencies, according to data security experts.

The NEM was split up and dispersed to several digital addresses.

The Metropolitan Police Department’s cybercrime division, which questioned the man on a voluntary basis, suspects several people were involved in converting the stolen NEM and is monitoring darknet sites and NEM transactions to identify them, the source said.

Following the massive theft of the digital money, data security specialists found an account believed to have been used by one of the perpetrators to trade the stolen NEM on the darknet.

Their analysis of money transfers from the account showed that NEM cryptocurrency worth more than ¥500 million was withdrawn on more than 200 occasions between early Thursday and Friday evening, based on the exchange rate at the time of the hacking attack.

Based on the current exchange rate, the converted currency is worth over ¥300 million, they said.