How many BTC were seized in relation to the shutdown of Silk Road?
According to this New York Times article of October 3, 2013:


  Investigators believe Mr. Ulbricht collected commissions of more than 600,000 bitcoins, the equivalent of $80 million, which they are trying to gain access to. So far, the authorities have seized 26,000 bitcoins, worth about $3.6 million, from escrow accounts into which Silk Road buyers placed funds.