(Reuters] – Federal prosecutors are investigating whether short-sellers tried to reduce stock prices through sharing damaging research reports in advance and illegal trading strategies, according to the Wall Street Journal.

According to a report, U.S. Justice Department officials have taken hardware and trading records, as well as private communications, in order to establish a broad conspiracy between investors betting against shares of corporations.

An FBI agent served Carson Block (NYSE:) with a search warrant in October. The report also stated that Block was the short-seller for Muddy Waters.

In early last year, subpoenas were issued by the Justice Department to many companies. This included requests for trade records, funds trading records, and other information. Reuters reported December that it issued a second series of subpoenas over the coming months.

Short-sellers or traders making profits on falling stock prices have come under fire from sky-high stock exchanges.