There can be any number of reasons the coin was moved:
- hacked by some 3rd party
- corruption by officers (https://news.bitcoin.com/rogue-silk-road-agent-admits-to-ste...)
- partner in crime moved them, with or without consent from suspect.
Ex: Being in the vicinity of a crime when it takes place may make you a suspect (aka "fishy"), but this alone is not enough to prove guilt.
All your comments in the thread are about "proving it," when, at the end of the day, it's up to 12 people in a box, most of whom don't know the first thing about bitcoin. Refusal to decrypt, wife moving Russia, etc... The government is going to make an extremely convincing case, with plenty of witnesses and all the time and money and lawyers they need. Meanwhile you'll be communicating with your defense lawyers from behind bars. You might be right -- maybe they can't prove any ill-intent -- but that's not a gamble with the odds in your favor.
- Can the prosecution show where and how Mr. X moved the funds while he was in jail?
- Can they show who he communicated with or ordered to abscond these funds?
- Can they identify who controls the funds now?
- Can they identify anyone else who may have had control of these funds while in their previous wallet?
The answer is basically no to any of those questions. This is simply because of the nature of crypto and mathematics; a set of seed words allows anyone to restore access on any machine, from anywhere on the planet.