Yes but Ross had really poor operational security. He reused identities across stack overflow. If you want to prove that someone had a private key stolen and ha

Yes but Ross had really poor operational security. He reused identities across stack overflow. If you want to prove that someone had a private key stolen and had poor operational security what this hypothetical person could do is as follows. 1. Takes the private key of the person in question. 2. Immediately sends an email to a fence or just sends the BTC to an exchange. 3. Takes the money. In a court case you could claim the following: The user that got their private keys stolen has record of a file containing a private key that they own which is older than the other user and has done at least one purchase with it. If the person who stole your private key has transactions that aren't older than the original owner that's how you could argue the case.