The grainy film captures the soldier as he shoots from his vantage point on top of the yellow stone building.
He fires more than once and then, suddenly, turns the rifle and points toward the camera lens.
The film ends – and so too ended the life of Ahmed Samir Assem.
The 26-year-old photographer for Egypt’s Al-Horia Wa Al-Adala newspaper was among a least 51 people killed when security forces opened fire on a large crowd that had camped outside the Egyptian army’s Republican Guard officers’ club in Cairo, where Mohammed Morsi, the deposed president, was believed to be in detention.
Mr. Assem had been on the scene as the pro-Muslim Brotherhood protesters knelt for prayer shortly before dawn on Monday morning.