Moussaoui eligible to die

Phase One of the Massoui trial has ended with the decision that he is eligible for the death penalty (from WaPo) :

A federal jury today found Zacarias Moussaoui eligible to die for his role in the Sept. 11, 2001 attacks, concluding that Moussaoui’s lies to federal agents paved the way for the deadliest terrorist strike in U.S. history.

Polimom has what my daughter refers to as “a bad feeling in my stomach” about this.
I’m uncomfortable with the decision — not because I’m against the death penalty (I’m not against it, as it happens). It’s because my understanding of capital punishment is that it applies to actual perpetrators. Consider:
Three guys plan to rob a bank. One of them kills a teller, the other drives the getaway car, but the third guy got arrested trying to steal the car they were supposed to use and sat the robbery out in jail. The shooter is up for the death penalty, the driver gets life in prison. What should happen to the guy that sat in jail that day?
I’m having a hard time picturing a death sentence for that third guy. To me, the main difference between the above scenario and Moussaoui’s case is that the crime was much, much bigger. The crime that galls us all.
Yet in spite of the fact that Moussaoui testified against himself as being part of the plot – he sat this out in jail. This feels a bit vigilante to me.
I hate these terrorists – including the slimy Moussaoui… but can America justify killing a man for something he didn’t do?

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Update: The Patriot News Clearinghouse’s entry at Daily Kos includes this:

“Felony Murder Rule – States that any death, which occurs during the commission or attempt to commit certain felonies, which include arson, rape or other sexual offenses, burglary, robbery or kidnapping, is first-degree murder and all participants in the felony can be held equally culpable, including those who did no harm, possessed no weapon, and did not intend to hurt anyone. Intent does not have to be proven for anything but the underlying felony. Even if, during the commission of the underlying felony, death occurs from fright, a heart attack for instance, it is still first-degree murder.”

Polimom’s still stuck on the question of whether Moussaoui can be considered a participant in the felony. Yes, he was in on the plot. Yes, he’s a terrorist who hates the United States and would have given his eye-teeth to have died on September 11. But a participant?
This, though, is really what’s at the heart of the matter:

The second advantage is that the Bush team has established a new rule that when terrorists are captured, they have a duty to provide intelligence to the US about their plot or pending attack and also the evidence to convict them.

Yeah. I can see that happening.