At the time the terms likely did not have statistically significant search volume. I'm not going to say he was the only one, but the other three might have been people who then corrected their search from "dcleaks" to "dc voltage leak" or something.

If you search for "[government agency] mailing address" three days before they receive anthrax in the mail, it isn't a slam dunk case. But if it was also mailed from your zip code, you had placed 6 phone calls to that agency in the prior month, etc. it makes you a pretty damn good candidate.