(Reuters) -U.S. authorities filed criminal and civil charges against prominent activist short seller Andrew Left on multiple counts of securities fraud for an alleged long-running market manipulation scheme, they said on Friday.

The criminal indictment, filed on Thursday, said Left “commented on publicly traded companies, asserting that the market incorrectly valued a company’s stock and advocating that the current price was too high or too low,” the Justice Department said in a statement.

The SEC filed separate civil charges against Left and Citron Capital LLC over what it described as a $20 million scheme to defraud followers.

Left, 54, of Boca Raton, Florida, used his Citron Research website and social media platforms to recommend long or short positions in 23 companies, telling followers they were consistent with his own positions, authorities said.

But then Left and Citron Capital quickly reversed those positions to capitalize on stock price movements, they said.

“The commentary routinely included sensationalized headlines and exaggerated language to maximize the reaction it would get from the stock market,” the Justice Department said.

A lawyer for Left did not respond immediately to a request for comment. He is expected to be arraigned in the coming weeks in United States District Court in downtown Los Angeles.