The Bitcoin network doesn't lend itself well to concealing that large an amount of money!However, the OP's question is a legitimate one and I have wondered myself if BTC could be used in a hostage scenario. Irrespective of the problem of getting one's hands on that many Bitcoins in one go it's hard to see how a mixing service could cover your tracks as the amount in question would be difficult to hide.Having said that the Bitcoin network isn't going anywhere so it might be possible to cash out small amounts at a time to live comfortably but I think you'd find LEO would be putting their best people on to tracing the flow of coins throughout the network to you. None of this is to say Bitcoins couldn't be used to extort money from people, I just doubt they could conceal a very large Ransom.Incidentally has anyone seen the 1994 Mel Gibson film "Ransom"? Gibson plays a millionaire whose son is kidnapped for a ransom of 2 million dollars. When he realises (correctly!) that the kidnappers have no motive to give his son back even if he pays up, Gibson's character instead offers the money as a bounty on the kidnappers' heads, offering to retract it if his son is returned unharmed. A rather drastic solution but under the circumstances I think it was his only option!V.