They can confiscate all they want, if Shavers would have wanted the data to be gone, it certainly would have been. I mean it's not exactly rocket science to use a shredder.
I'm not so sure about that, for such a low-traffic site its much more likely he used shared-hosting (or a VPS) instead of his own dedicated server, and every hosting provider holds backups of its customers data. So even if he quickly deleted everything, that company would be able to provide the SEC with a recent backup.