Suppose you have the Bitcoin on a local wallet, and your computer crashed, losing all the private keys (perhaps presenting the requisite Apple Store receipts when you took it down to the store to get repaired). A bit like losing your cash in a fire; computers do crash quite a bit. Not a lawyer, but I think something like that might be difficult to disprove in court. On the other hand, subsequent spending from those addresses would then be monitored. So perhaps best to report that computer lost/stolen.