On December 24th, 2008, Hamas declared war on Israel. As Ma'an reported at the time,
The military wing affiliated to Hamas, Al-Qassam Brigades released a statement on Thursday morning briefing the group's military activities over the first twenty four hours of an operation they called "Oil Stain" which started Wednesday morning.Indeed, Hamas' Al Qassam Brigades website still has the original announcement of Operation Oil Stain (autotranslated as Oil Slick.)
According to the statement, a total of 87 shells have been fired at Israeli targets bordering the Gaza Strip including 54 mortar shells, 31 homemade projectiles which Hamas calls "Qassam", and two Soviet-made Grad missiles.
Al-Qassa Brigades threatened to enlarge the "Oil Stain" to get more thousands of Israelis "under fire". The group asserted that its fighters are "far greater than surrendering to Israeli threats and that they became much more prepared to counter Israeli aggression and to defend themselves than in the past."
However, in their reports about the war, Amnesty International, Human Rights Watch and the Goldstone Report all consider December 27th the first day of the war - the day that Israel struck back heavily.
Normally, if one party attacks another and even names the operation, that would be considered, objectively, the beginning of the war. Hamas continued calling the war "Oil Stain" for a full week before it abandoned the term.
When NGOs decide that the war began three days later than it really did, they are establishing a framework that damns Israel before they even write a word about the issues. It is a false framework. It makes Israel appear to be the aggressor and not as if it is reacting to deliberate and planned Hamas actions.
And those Hamas actions would be considered grave war crimes, as they targeted civilians. (Hamas press releases even brag about how Israelis are forced to go to bomb shelters!)
Israel didn't start the war, and every NGO report that says it did on December 27th is guilty of bias.