The Comprehensive Forfeiture Act of 1984 allows it and US v. Monsanto upheld it. Since this is being prosecuted under RICO, it's lawful and Constitutional. Let's not forget that the US is only one of at least five countries involved in this case. No one has accused or has evidence that Larry Page has done anything illegal. But if there was evidence that page is violating RICO, then try can take his stuff until trial as well. As far as innocent until proven guilty, that actually isn't in the Constitution, it's based in English Common Law -- Dotcom's right aren't being violated as he is getting due process. Of course, te current situation of extradition requires a much lower standard of proof, the standard here is whether or not there is evidence that warrants a trial; effectively like a grand jury deliberation.