Ilya Lichelman, who pleaded guilty last year in the Bitfinex case, is now a U.S. witness and is helping federal prosecutors prosecute Bitcoin Fog, one of the coin-mixing services it once used to hide assets. Ilya Lichelman pleaded guilty last year to involvement in the $3.6 billion Bitfinex hack; the U.S. Department of Justice seized billions in cryptocurrency in the Bitfinex case, an unprecedented move. (CoinDesk)