They simply can't confiscate anything unless they are given the private keys. Theoretically impossible.
That's what some people commenting here fail to understand. None of the confiscated Bitcoins were taken by force, i.e. cracked. I doubt they (the authorities) would even try to break into your wallet. They would rather pressure you into giving it up, just as they did with DPR.
That is different. Imagine a criminal who stole some BTC from you. If he/she gets killed during the arrest, the government can't possibly give your BTC back.