The U.S. Securities and Exchange Commission (SEC) introduced a sealed motion with more than 31 exhibits in its case against crypto exchange Binance on Monday. Industry watchers believe that the move bodes ill for the firm, and likely implies it is the subject of a criminal probe from the U.S. Department of Justice (DOJ).

The SEC’s case against Binance is a civil case that alleges the exchange, its U.S. subsidiary Binance.US, and CEO Changpeng Zhao violated U.S. securities laws. However, according to former SEC official John Reed Stark, the introduction of sealed documents likely means they pertain to “secret details” about a criminal investigation or prosecution by the DOJ.

“Also, in connection with its investigation of Binance, U.S. DOJ may be working with confidential informants or whistleblowers, may have wires or other listening devices in place or may even have an active arrest warrant or undercover operation in the works,” said Stark. 

He speculated that the SEC’s rare secret filing touches upon non-public information about Binance’s money laundering allegations or other criminal conduct. In his view, Binance is unlikely to oppose the sealing of these documents on the fear of these allegations or potential evidence becoming public knowledge.

“In my almost 20 years in the SEC Enforcement Division, including 11 years as Chief of the SEC’s Office of Internet Enforcement, our team worked on and led a broad range of SEC investigations which involved parallel U.S. DOJ investigations and lots of litigation — and I can’t recall ever seeking to file a motion or any other court document under seal,” said Stark.