And the seizure seems to be total, not just US. I went to BP using TOR and a VPN, and the TOR circuit I was on would have given an IP address in Europe; I still got the FBI seizure notice page.

Here's a link about this:  

It's a 93-count sealed indictment.  Part of what they released says they have evidence of BP staff editing otherwise-illegal content and making it legal.  This contradicts the assertion that "We just let people post.  We're a message board."  They also seized internal emails demonstrating that the people running BP were knowledgeable that it was occurring and helped it continue.  The founders started offloading assets in March, probably trying to avoid any seizure.

If the government can demonstrate that the founders knew of the investigation and took preparations like offloading assets and destroying evidence, they can be charged under SOX and probably pick up some obstruction charges.