The Department of Justice filed its complaint against 19-year-old Boston Marathon bombing suspect Dzhokhar Tsarnaev on Monday, charging the U.S. citizen in his hospital bed on two charges: "use of a weapon of mass destruction" and "malicious destruction of property resulting in death." He'll be tried in a U.S. federal court — not as an enemy combatant, as some lawmakers had pushed for — and faces the possibility of life in prison. The WMD charge could result in the death penalty, raising a strange question in a case sure to be full of precedents in how America prosecutes terrorism: Do bombs made in kitchen pressure cookers, like the ones the Tsarnaev brothers allegedly planted at the Boston Marathon and then hurled at the authorities in a shootout, now count as weapons of mass destruction?

There's no debating that two explosive devices killed three people and injured over 180 more a week ago in Boston's Copley Square. But Americans are used to hearing about WMDs in the case of Iraq (falsely), or Syria (reportedly), or Iran and North Korea (depending on which hubristic world leader you believe). But where do pressure cookers fall in the evolving legal definition of WMDs these days? And will that evolution hinder the prosecution in proving that the bombs in Boston fit into the legal justification for the charges? We investigated.

First off, to be sure, everyone knows what a pressure cooker is — even Gov. Deval Patrick, to whom Wolf Blitzer showed off one of the household devices shortly after CNN's "arrest" debacle last Wednesday:

Now, CNN aside, here's what we actually know, as detailed in the Justice Department complaint: The brothers are charged with making IED devices out of the cookers:

A preliminary examination of the remains of the explosive devices that were used at the Boston Marathon revealed that they were low-grade explosives that were housed in pressure cookers. Both pressure cookers were of the same brand. The pressure cookers also contained metallic BBs and nails. Many of the BBs were contained within an adhesive material. The explosives contained green-colored hobby fuse. 

The pressure cooker brand has yet to be revealed, but that charge seems to align with and official FBI update last week that "fragments of nails that could have been contained in a pressure cooker" and carried in black backpacks. There was also, according to photos of the devices released by the agency, a homemade battery from Tenergy, which was aiding in the investigation. Those same FBI photos appear to show the remains of a pressure cooker at the scene:

So, it now appears that prosecutors for the U.S. will argue that the pressure cookers qualify as material modified to expel a projectile — Boston doctors treating victims reported pulling BBs and nails out of victims — and therefore align with the current definition of a WMD. 

Indeed, the F.B.I.'s official definition of a weapon of mass destruction covers chemical, biological, and nuclear weapons. Except the Tsarnaev brothers didn't use any of those things. And as Wired's Spencer Ackerman noted last month, that's been a point of some contention:

In fact, as a fascinating paper by W. Seth Carus at the National Defense University shows (.pdf), the Defense Department’s definition of the term has long been problematic. For years, its official definition included “high explosives,” to make it consistent with the federal statute that Harroun ran up against. But “most military weaponry relies on high explosive charges,” Carus writes, “meaning that even the mortars and grenades used by infantrymen might qualify as WMD.” The doctrinal answer was ultimately to limit the definition to “chemical, biological, radiological and nuclear weapons capable of a high order of destruction or causing mass casualties.”

But clearly those weapons are not created equal.

That's where the "destructive device" clause comes in. The FBI further classifies a WMD as "a destructive device as determined by section 921" — and that section is wide ranging:

(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled.

Section A includes bombs, grenades, rocket propellers, missiles, and mines. Section B is pretty vague, too:

(B) any type of weapon (other than a shotgun or a shotgun shell which the Attorney General finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, and which has any barrel with a bore of more than one-half inch in diamete...

The always reliable explainers over at Cornell's law blog put that in layman's terms (we've italicized the relevant parts):

(4) The term “destructive device” means—

(A) any explosive, incendiary, or poison gas— (i) bomb, (ii) grenade, (iii) rocket having a propellant charge of more than four ounces, (iv) missile having an explosive or incendiary charge of more than one-quarter ounce, (v) mine, or (vi) device similar to any of the devices described in the preceding clauses;

(B) any type of weapon (other than a shotgun or a shotgun shell which the Attorney General finds is generally recognized as particularly suitable for sporting purposes) by whatever name known which will, or which may be readily converted to, expel a projectile by the action of an explosive or other propellant, and which has any barrel with a bore of more than one-half inch in diameter; and

(C) any combination of parts either designed or intended for use in converting any device into any destructive device described in subparagraph (A) or (B) and from which a destructive device may be readily assembled.

The types of devices the Tsarnaev brothers allegedly used to bomb the marathon would likely qualify under this definition. In the shootout in Watertown, Massachusetts, "the Tsarnaev brothers hurled something at the officers — apparently a pressure cooker bomb — and there was a tremendous explosion," the local police chief told The Boston Globe. Whether that counts under these charges remains to be seen, but the single WMD charge may be enough for prosecutors to seek capital punishment — a decision that would come after the initial trial but that could see Dzhokhar Tsarnaev's life come to an end in the same death chamber as Timothy McVeigh.