I know that, but Zawahiri’s brother knew about it earlier and called out the demonstrators to show up that morning with that as the excuse.
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His demonstration was planned before that day, and was in response to a video [though the press was not certain which video he was talking about as there was another one out there] and the preplanned demonstration is why the embassy was understaffed in Cairo and the nonesentials had been sent home.
There were several reasons the protesters were there in Cairo the least of which was the ‘video.’ Yes, the embassy knew it was coming.