Kaji :

This one is easy. On one hand, Kaji is loveable, funny, charming. On the other hand, he seems to serve many masters, his loyality is divided (IS he loyal to anyone ?) and there is a certain touch of evil. This double-faced nature is Chokhmah.
Chockmah's illusion is independence. Kaji is loyal to noone aside himself, thus showing a strong will to be independent. Kaji's way of taking-it-easy with others, flirting, having fun and such is equal to Misato's habit's (though it is not clear if he became that way after she left him or if he was like that in the first place), showing the Qlippah of Chockmah : arbitrariness.
Kaji is somehow stuck inbetween good (virtue) and evil (vice), he would have been able do do considerably evil things, but didn't. This may be because he was still in love with Misato and wanted to show her the truth behind NERV and SEELE.
The answer to the question who killed Kaji could reveal which side he pissed of most, thus indicating maybe a decision he made towards "good" or "evil". He knew his assasin, so Misato is one of the suspects, but she seemed to be unaware of his death for a certain time. The most promising interpretation would be that SEELE ordered his death ... but I think Gendo is a good bet as well.