Democrats notified the FBI over concerns Russia is "laundering" intelligence directed against former Vice President Joe Biden through a GOP-led Senate committee.
Paul Erickson was indicted in his home state of South Dakota on 11 counts of money laundering and wire fraud.
Natalia Veselnitskaya is accused of obstructing justice in a New York-based money laundering investigation that ended in 2017.
Mueller filed a previous indictment against them last October.
The four men had been jailed on drug and fraud charges.
Wilbur Ross's role as vice-chairman of the Bank of Cyprus has also drawn scrutiny.
Online giveaway of bitcoins prompts speculation of elaborate money laundering scheme.
The U.S. has declared the country a "primary money laundering concern."
Foreign companies will have to make their U.K. property portfolios public.
At least three people have been arrested as part of a larger investigation.
The scandal has gripped Russians online, but state media have remained quiet.