User blog comment:DeathGodPrayer/Talk About What You Want!/@comment-98.26.119.147-20140114220805/@comment-98.26.119.147-20140115013629

@B214 But he was the one that put Diodora in a position where Diodora could not stand or at least try and fight Shalba which could have possibly angered them and with shalba's death they just placed on Issei because he is still alive.

and although unlikely I think it wouldn't be impossible for the astaroth clan to be smart and get information to the khaos brigade along with the Vassago.