You’d better be careful about what souvenirs you bring home from your next hike. You could be endangering Homeland Security without even knowing about it, you agricultural bioterrorist, you.
There is no requirement that the owners of electronic equipment be suspected of any crime or any other form of wrongdoing. Homeland Security will take your computer at will, without explanation, just because it wants to, and you might never get it back.
It seems likely, given the suicide, that Ivins was involved in one of the very few bioterrorist attacks ever to take place, but there will never be a trial now, and so we may never know for sure. In criminal investigations, things are often not what they seem.