Reaction of governments
The reaction of major governments, including significant powers like the US, UK,RU,NL and many more, proves that they are confident that this accident was caused by something sinister which could be easily repeated, the same threat is clearly still present at that airport and in the entire region, both in terms of culprit and technique used: this matches with the theory of an airport worker who successfully loaded explosive into the cargo hold of this aircraft. The terrorists, very likely belonging to ISIS in Sinai, did not know if their newly found technique would have been successful until the explosion was triggered hence the lack of further messages from ISIS, after they released their video, as they do not want to disclose any more info about the modality of loading and detonation, obviously they are fully aware now that they can do it again and very easily. Intelligence agencies were reported by the media to have listened into terrorists' conversations showing a sense of victory, similar to Osama Bin Laden when he watched the Twin Towers collapsing, no terrorist knew for sure that the explosion would have actually brought down the plane, they simply did not know if they would have been successful or not as it was something never tested before inside a real flying plane: imagine if the explosive was hidden inside a scuba tank, as a guess, this has never been tested before and maybe this is why the investigators will probably not find any unusual and unexpected material amongst debris on the ground nor signs of explosives as some types do not leave traces. A possible scenario in my opinion which would validate the unprecedented decisions recently taken by major governments against Egypt.