Israel killed Jabari because the so called ceasefire never existed and Israel has been under constant rocket fire from Gaza. The amount of rockets increased in the last few days and then and only in response to the increased rocket attacks, the Israeli government decided to retaliate. So the question that has to be asked is why they have waited at all, or maybe why the international media seems to very conveniently ignore any kind of aggression from Gaza.
Iranian parliamentary panel gives conditional nod to nuke deal (Reuters)
from the article: LIVE BLOG: Day 2 of Israel-Gaza conflict 2012