UN finds Gaza killings were a crime against humanity, page-39

Most of the news articles and information from knowledgeable people has long gone.
But Israel had lots of agents operating in Gaza, and they would have known well in advance of the preparations for the attack, it would have been hard to hide.
secondly, the security fences between Gaza and Israel are so intensely monitored that a mouse cannot approach undetected.

There are military personnel stationed right along the border.

So, Israeli security had no knowledge of the plans and the buildup, the terrorists approached the fence and broke through undetected and attacked Israeli citizens freely for hours before their defense forces sprung into action.

When Israeli citizens were held hostage by Hamas terrorists, they were shot by the Israeli helicopter gunships along with the Hamas terrorists.