TOKYO (Kyodo) -- A North Korea-linked hacker group stole digital assets worth 48.2 billion yen ($307 million) from Tokyo-based cryptocurrency exchange DMM Bitcoin Co. in May, Japanese police said Tuesday.

The hacker group was identified by the police as TraderTraitor following an investigation conducted in collaboration with the U.S. Department of Defense and the Federal Bureau of Investigation.

DMM Bitcoin said earlier this month it will go out of business after suspending some of its services following the detection of the unauthorized leakage of funds on May 31.

The police tracked the flow of stolen bitcoin to an account managed by the group, which is suspected to be linked to the Lazarus hacking group allegedly sponsored by the North Korean government.

The investigation found that an employee at a company that manages DMM Bitcoin's cryptocurrency accounts was contacted via the LinkedIn social network by a person purporting to be a headhunter.

The perpetrator then breached the wallet management system by planting malware and falsified transaction amounts as well as the destinations of remittances, the police said.

In September, Japan's Financial Services Agency ordered the exchange to improve operations, saying its risk management structure was inadequate.

No customers suffered financial damage as the exchange secured 55 billion yen from a group firm to cover the lost assets.

The police, the FBI, and other U.S. government and international partners will "continue to expose and combat North Korea's use of illicit activities," including cybercrime and cryptocurrency theft, to generate revenue for the regime, they said in a statement.