On Friday, as Egyptians sympathetic to now-deposed President Mohamed Morsi protested in front of the Republican Guard headquarters in Cairo, where he is believed to be held, security forces opened fire. At least one man was killed, his death confirmed by a video that captured the violent and disturbing moment.

In a day of confusion and violence, with crowds of people in the streets to support or oppose the military's decision on Wednesday to push out Morsi, this one moment may symbolize, for many, the wider crackdown on members of the Muslim Brotherhood. An emerging view among Islamists is that the military was not just deposing Morsi but moving against the Muslim Brotherhood, which backed him. That belief has perhaps been crystallized by this video, which is circulating widely on Egyptian social media and runs the risk of worsening the outrage felt by many Islamists and the deep divisions between Morsi's supporters and his opponents.

Egypt's Muslim Brotherhood has endured decades of brutal repression at the hands of the military and the three military dictators who preceded Morsi. Though vast numbers of Egyptians supported the military's ouster of Morsi, whose rule had been growing less and less democratic, Friday's violence could exacerbate a sense among Islamists that they are unfairly persecuted and excluded from Egypt's nascent democratic experiment. As long as Islamists believe they are barred from participating in what they see as a falsely democratic system, they will likely seek other avenues to express their political will. That could mean more protests and perhaps violence.

Of course, we don't know the full story of this shooting in Cairo. Maybe a single member of the security forces acted against orders or felt physically threatened by the crowd. But let's remember the crackdowns by security forces during the January and February 2011 protests against then-president Hosni Mubarak. The shooting of protesters deepened popular Egyptian perceptions – and international perceptions – that the government had to enforce its will through violence.

The video is below. Warning: the video is violent and graphic. Readers are cautioned not to watch if they find such scenes too disturbing.