Manhattan federal prosecutors served subpoenas to several Bitcoin exchanges this winter, demanding customer-transaction logs and materials related to the solicitation of investors. The investigation is reportedly in an early stage.
The Journal also reports that prosecutors and FBI agents are examining whether Mt. Gox and other major exchanges processed transactions connected to Silk Road. They almost certainly did, of course, as the major online exchanges were regularly used by prominent Silk Roaders along with offline exchanges like LocalBitcoins.com.
The newly unveiled investigation follows Mt. Gox's suspension of trading in February after the disappearance of approximately $470 million worth of bitcoins.