They didn't just let it happen, what the picture shows is all the cars Israel says Hamas burned, but Hamas does not have the means to inflict that damage, they simply do not have weapons capable of doing that. Israel mowed down their own people with apache helicopters to blame Hamas and justify the genocide.
They've been looking for an answer to the Palestinian question for 75 years, and this was just what they needed.
The thing is, none of this is new, we've had the evidence (and testimony) that they killed their own people since day one, not to mention the genocidal intent expressed nonstop and the acting on it. No one has the credibility to say they didn't know, no one can say they didn't know the extent of the genocide, no less anyone in a position of power. Just pure evil, and everyone who preached at us about human rights is still to this day celebrating and congratulating Israeli leaders. Nazis, the lot of them.