> "The DOJ said it was able to seize the funds after an FBI search warrant of one of Lichtenstein's cloud storage accounts found a file containing cryptocurrency addresses and their corresponding private key that granted access to funds stored within."
That makes sense, and of course storing them in cloud storage was a bad idea. However they could have only obtained the warrant /after/ they pretty much knew Lichtenstein was the culprit.
How did they determine Lichtenstein was the person who had the bitcoins?