Authorities in Japan are reportedly targeting individuals for their alleged involvement in the January 2018 hack of the Coincheck crypto exchange.

According to a Jan. 22 report from Japanese news outlet Nikkei Asia, police have arrested or referred roughly 30 people in Japan to the local prosecutors’ office for their alleged role in hacking one of the country’s cryptocurrency exchanges. In January 2018, hackers stole roughly $534 million worth of NEM (XEM) from Coincheck in what was — and still is — the largest hack of a crypto exchange.

Nikkei Asia claims that according to an unnamed source, investigators “traced the accounts at conventional cryptocurrency exchanges through which the hacked NEM was converted” to identify the 30 people. The news outlet stated that the NEM tokens in cases involving the individuals may total as much as 20 billion yen — roughly $193 million at the time of publication.

Since the attacks occurred three years ago, investigators have alleged that Russian hackers may have been partially responsible for infecting the personal computers of Coincheck employees with a virus. The virus could have enabled hackers to take over the infected computers and operate them remotely.

Until now, Japanese authorities had made few arrests in connection with the Coincheck hack. In March, local police arrested two men who allegedly purchased some of the stolen NEM on a darknet marketplace shortly after the attack occurred. According to the police, the two knew the origin of the funds but still chose to purchase the tokens at a sizable discount.