Everyone here talking about how this definition is stupid is seriously missing the point. Just because the legal use of a term doesn't fit in with your conception of what a WMD is doesn't make it a stupid definition. I think it's clear that the federal government just wanted a separate criminal category for explosives and other extremely hazardous materials (chemical and biological).

Seriously, this should not be the first time that some of you guys have encountered a legal term that doesn't match up with the colloquial sense of the term.

And we shouldn't be predicating crimes on the competence of their perpetrators - their pressure cooker bombs did injure more than a hundred people. Had they engineered it optimally, they likely could have killed tens of more people.