Back up the claim how? The raw intelligence is classified, no doubt. All anyone ever gets is public statements and watered down facts.

Israel is a democracy though and has traditions of open government and of prosecuting war criminals. Hamas is a far right theocratic authoritarian regime that rules by assassination and wanton use of human shields, i.e., literally building massive tunnel systems under every city and using them to conduct decades of terror attack and indiscriminate rocket attacks in civilian targets. Whenever a bunch of Palestinian’s died, usually Israel says “well some of them were Hamas.” Hamas on the other hand insists every time that none of the dead are Hamas. For that reason, Israel is more credible.