The head of the Hamas military wing Ahmed al-Jabari had just received the draft of a permanent truce agreement with Israel, when his car was blasted by the Israeli strike that killed him, Israeli peace activist Gershon Baskin told Haaretz.
Baskin, who played a crucial role in the negotiations with Hamas that lead to the release of abducted Israeli soldier Gilad Schalit, told the Tel Aviv newspaper that he had been working with some success on the text of an agreement with Hamas, Egypt and Israeli representatives.
"I think that they [Israeli authorities] have made a strategic mistake, which will cost the lives of quite a number of innocent people on both sides. This blood could have been spared," Baskin told Haaretz.
"His [Jabari's] assassination killed the possibility of achieving a truce."
The Founder of Israel-Palestine conflict resolution think tank IPCRI - Israel/Palestine Centre for Research and Information - Baskin, met Jabari during the Schalit negotiations and kept communication channel with Hamas hierarchies open ever since.
According to Baskin, Jabari was "not an angel and not a righteous man of peace," but had however reached the conclusion that the continuous hostilities between Hamas and Israel were detrimental to both parties and to Gaza's people.
Baskin said he had been spinning trilateral negotiations between Hamas, Israeli and Egyptian officials that finally produced a truce agreement draft.
The draft was submitted to Israeli Defense Minister Ehud Barak and an inter-ministry committee was established to canvass the text.
"In Israel they decided not to decide," Baskin said. Then Jabari was killed.
"This is sad for me. I am seeing people getting killed and that is what is making me sad. I tell myself that with every person who is killed we are engendering the next generation of haters and terrorists."
"Those who made the decision must be judged by the voters, but to my regret they will get more votes because of this."
Israel is to hold parliamentary elections in January 2013.
Israel said Jabari's killing was just the beginning of a broader offensive called Pillar of Defence, launched after days of rocket fire from the Gaza Strip.
Egypt harshly condemned the Israeli "aggression" against Gaza and called recalling his ambassador from Jerusalem.
Israel's neighbour is ruled by the Muslim Brotherhood's Freedom and Justice Party, which is considered Hamas' ideological counterpart.