FBI agents have arrested research analyst John Kinnucan at his Oregon home on Thursday evening, and is being detained overnight.
Details of the charges will be made public on Friday morning after the indictment is unsealed. A source told CNBC the charges involved securities fraud.
Recent allegations that Kinnucan made threats against FBI agents, assistant U.S. attorneys and cooperating witnesses are understood to be not part of the charges, although they may be raised during a bail hearing on Friday.
Kinnucan, who in late 2010 sent an email to his clients that he turned down FBI's wiretap request, was subpoenaed by the government in December last year.