I read the original Bloomberg report on this a few days ago. It is the source this article is referencing.
This one line in the report ..."said the people, who asked not to be identified" arouses my suspicions as to the validity of this claim that a DOJ investigation is underway.
Cryptocurrencies are regulated by the "Commodity Futures Trading Comission" (FTC) and the "Securities Exchange Commission" (SEC). Each of which have their own investigative branches.. If an investigation was opened it would be opened by the FTC or SEC not the DOJ. However the DOJ would prosecute if charges are filed. If someone out there is more versed in the function of DOJ involvement in such matters I'm open to your input.