Also one wonders what is done with the 'evidence' after the case. I could imagine the FBI simply deleting the wallets but does anyone know their actual policy?
In the US, law enforcement gets to keep a portion of whatever they seize. You can bet your ass they will not destroy millions worth of assets -- entire departments will get bonuses for years for this.
Law requires them to liquidate the assets through auctions, they cannot simply sell them at an exchange, or set a price for them and sell them at that price. There are plenty of companies that specialize in organizing such events.
Pretty sure whatever their policy is, it isn't "throw away $150million of seized assets"
What does the FBI or other agencies do with intercepted drug money and criminal possessions? Drugs get destroyed, that much I know, but not sure about the other stuff.
Bitcoin is not "fiat currency" by the most common definition(currency whose value is supported by the mandate -- or "fiat" -- of a government for its use in certain domains, but which is neither a directly-useful commodity on its own nor backed by a promise of exchange for a commodity.)
Bitcoin is "fiat currency" by another broader definition ("currency that is neither a generally-useful commodity on its own nor backed by a promise of exchange for a commodity"), which has historically largely been equivalent to the more common definition, because prior to Bitcoin and similar cryptocurrencies, no one was using unbacked currency that weren't supported by government fiat.
Its probably better to use a different term for the broader definition, since there is no fiat necessarily involved, there are meaningful differences between unbacked currencies supported by government fiat and those that aren't, and there are now meaningful examples of unbacked currencies without the support of a government fiat.
http://www.google.com/trends/explore#q=%22fiat%20currency%22
I ask because most of these articles are trying to shock you with the exchange value rather than the BTC value.