U.S. prosecutors secured another conviction this week in a business email compromise (BEC) scheme that dates back to 2017.

Nigerian national Henry Onyedikachi Echefu, 32, pleaded guilty Monday to conspiracy to commit wire fraud and conspiracy to commit money laundering, the Department of Justice (DOJ) said.

Echefu was in South Africa at the time of the cybercrimes, and was part of a ring that included two other Nigerians and co-conspirators in Maryland, prosecutors said. Overall, U.S. officials have estimated the operation stole $6 million.

South African media reported that the Nigerian trio allegedly operated out of a luxury residence in the Johannesburg area.

One of the three, Kosi Goodness Simon-Ebo, pleaded guilty in the U.S. in September to his part in the scheme and received an 18-month prison sentence.

The other Nigerian indicted in the case, James Junior Aliyu — who allegedly used the aliases “Old Soldier” and “Ghost” — is reportedly still in custody in South Africa. U.S. and South African officials did not immediately reply to requests for information about Aliyu’s current status.

Echefu faces up to 20 years in federal prison. Sentencing is scheduled for May 23.

With the other suspects, he “gained unauthorized access to email accounts associated with individuals and businesses targeted by the conspirators and sent false wiring instructions to the victims’ email accounts from ‘spoofed’ emails, which are emails with forged sender addresses, to deceive the victims into sending money to bank accounts controlled by perpetrators of the scheme, called ‘drop accounts,’” the DOJ said.

Last year the FBI estimated that from 2013 to 2022, BEC scams cost victims a total of at least $50 billion. For 2023 alone, the bureau estimated $2.9 billion.