We tend to associate weapons of mass destruction with nuclear bombs or deadly arsenals of chemical or biological agents.

The Boston marathon attack was horrific and deadly. But, as legal scholar Jonathan Adler noted on Volokh Conspiracy, it may have struck some as odd that the homemade bomb allegedly detonated by Dzhokhar Tsarnaev qualifies as a “weapon of mass destruction” under the law used to charge him.

Here’s an explanation.

When Congress drafted the Violent Crime Control and Law Enforcement Act of 1994, it adopted a fairly broad definition of WMDs.

Under that statute, a “destructive device” is considered to be a WMD. And an “explosive” qualifies as such a device, among other types of weapons. (Oklahoma City bomber Timothy McVeigh was prosecuted under the same statute.)

http://blogs.wsj.com/law/2013/04/23/why-a-homemade-bomb-is-a-weapon-of-mass-destruction/