Four men have been charged in U.S. federal court for their alleged involvement in a so-called pig butchering scheme that stole more than $80 million from unwitting victims.

According to the Department of Justice, three California residents — Lu Zhang, 36; Justin Walker, 31; and Joseph Wong, 32 — along with Illinois resident Hailong Zhu, 40, are charged with “conspiracy to commit money laundering, concealment money laundering, and international money laundering.”

Zhang and Walker were arrested on Tuesday and appeared in a Los Angeles district court, while their alleged co-conspirators remain at-large. The four men are accused of opening shell companies and bank accounts to launder cryptocurrency procured through the pig butchering scams, where fraudsters form relationships with victims on social media, dating sites or messaging platforms.

“Scammers initiate relationships with victims and slowly gain their trust, eventually introducing the idea of making a business investment using cryptocurrency,” the DOJ wrote.

After victims make an “investment” through fraudulent platforms controlled by the scammers it initially appeared that they were making a profit.

“Ultimately, the victims are unable to withdraw or recover their money, often resulting in significant losses for the victims,” the DOJ wrote. According to the indictment, victims were also targeted by tech support scams as part of the scheme.

Zhu allegedly registered two shell companies called Sea Dragon Trading and Sea Dragon Remodel. Between September 2022 and March 2023, he and co-conspirators allegedly funneled money through accounts with JPMorgan Chase and Bank of America, which were linked to the shell companies.

At least 284 transactions were made through the scams, with more than $20 million “directly deposited into bank accounts associated with the defendants.”

Zhang and Walker face up to 20 years in prison.

In 2022, according to the FBI, investment fraud caused the highest losses of any type of scam in the United States.

“Frauds involving cryptocurrency, including pig butchering, represented most of these scams, increasing 183% from 2021 to $2.57 billion in reported losses last year,” the DOJ wrote. In April, the agency announced the seizure of more than $112 million linked to cryptocurrency investment fraud.

The investment scam industry has metastasized into a global threat, with organized crime syndicates operating scamming compounds throughout Southeast Asia and the industry spreading as far as South America, Interpol recently warned.

In early December, a Nigerian man was sentenced by the country’s Federal High Court to three years in prison for carrying out pig butchering scams, using a fraudulent investment platform to defraud victims in 13 countries — including the U.S., Germany, India and South Africa — of more than a half-million dollars.