A majority of the jury members actually DID go for the death penalty. One of them opposed it. They question is why? I do not know.
1) They believed in humanity and do not believe in death penalty
This is possible but really not an allowed option. People that are against the death penalty are not allowed to be part of a jury in a death penalty trial.
(2) They did not wish to let Moussanoui full fill his wish of being a martyr
That is REALPOLITIK, a court are supposed to be about LAW however, not realpolitik.
(3) They considered the evidence presented by both sides, and felt that that is the correct verdict following the judge's analysis and direction.
This is what a court case really are about, the reason it "should" be, it is not neccessary true thou.
(4) They felt that life imprisonment is a better punishment for Moussaoui as he will be tortured in any American prison by the guards and the prisoners alike for the rest of his life.
Misstreatment of prisoners are a sad reality, illegal but it does happen. To sentence someone to prison inorder to be misstreated are hardly legal, or moral.
(5) Cheaper than appeal etc if death sentence was passed.
This is the realpolitik argument again.
(6) Others?
Possible, but what do we know what happened in ONE persons chain of thoughts?
I mite add that I myself are against the death penalty and it was abolished in my contry 1921.