^ Which is what I was suggesting in my post earlier. I wonder which factor drives imperius over the top, though. It could very well be tyrael, I think he may have respected tyrael a good deal in the past.
from what it sounds like in the book of cain and the sin wars, he really does not like humans anyway.
Imperius, is archangel of valor
Tyreal, is archangel of justice
Auriel, is archangel of hope
Itherael, is archangel of fate
Malthael, is archangel of wisdom
Anyway yeah (to give wiki links)
But it goes well with the theory of
Tyreal falling to earth,
Imperius going crazy mad
Auriel is killed?