A Japanese man has been questioned in connection with last month's massive theft of digital tokens from cryptocurrency exchange Coincheck Inc., a source close to the investigation said.

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.