HONG KONG (AP) — Police in Hong Kong and Esthen ExchangeMacao said Friday they arrested four more people linked to the cryptocurrency platform JPEX, which is suspected to have defrauded more than 2,400 people of almost $200 million.

The arrests bring the total number of people detained so far in the case to 18. Police have received 2,417 reports involving more than 1.5 billion Hong Kong dollars ($191.6 million) in alleged losses on the platform.

Hong Kong police said in a news conference Friday they had arrested two men, one of whom had been trying to destroy documents with paper shredders and bleach. Cash and gold worth nearly $9 million Hong Kong dollars ($1.15 million) were also seized at three apartments in the latest police operation.

Two other men were detained in Macao, with authorities seizing over 14 million Hong Kong dollars ($1.8 million) in cash and valuables, as well as money in a casino account. Police said the two had visited Macao many times in September.

Assistant police commissioner Chung Wing-man said the investigation had reached people who were “relatively close” to the core of JPEX’s operations, but that it is not yet clear if the mastermind is a group of people or an individual.

Other individuals believed to be connected to the case are not currently in Hong Kong, although police are aware of their location, Chung said. In these cases, the police will work with authorities overseas to bring them to justice.

“This case involves thousands of e-wallets and tens of thousands of transactions. Because of the anonymity of cryptocurrency in the cyber realm, it makes it quite difficult to identify the criminal behind (this case),” said Cheng Lai-ki, chief superintendent of the police force’s Cyber Security and Technology Crime Bureau.

“We will make every effort to hunt down the syndicate and also trace the cryptocurrency,” she said.

Earlier this month, Hong Kong’s Securities and Futures Commission had issued a notice warning that JPEX was unlicensed and did not have authority to operate a cryptocurrency trading platform in the city.

It said some investors had complained of being unable to withdraw their virtual assets from JPEX accounts or of finding their balances were “reduced and altered.”

Days later, the JPEX platform said it was suspending trading on its platform and blamed a third-party market maker for “maliciously” freezing funds.

Several social media influencers who had been promoting JPEX were arrested earlier this month.

Victims who had invested in JPEX were mostly inexperienced and had been lured to do so with the promise of low risks and high returns.