They'd probably have to prove you were doing this because of a pending investigation against yourself. What if you were just using it because you didn't want Zee Germans (or some other personal adversary) getting access to your data?

You mean destruction of evidence or obstruction of justice. Contempt of court likely doesn't apply unless you were asked to turn the evidence over yourself and destroyed it.

It is likely that you could be. But as with all criminal proceedings they'd need to prove it beyond a reasonable doubt. If the KillUSB software itself was unrecoverable it might prove difficult.