Behind the violence may be a rumor.
Like many recent episodes of Muslim-Christian violence here, the strife began over rumors of an interfaith marriage. Muslims in the neighborhood said a former Christian had left the church and married a Muslim. They said they had heard that she had been abducted and detained inside the church of St. Minas against her will, reflecting a pattern of accusations that has recurred in several recent episodes of sectarian conflict.
So, let's see, Christians believed rumors that Jews kidnapped them to use their blood during Passover, so they murdered Jews. Today, Muslims believe rumors that a convert is held against her will, so they go after Christians. Christians stand up for themselves. Christians and Muslims die as a result. Churches are burned.
The usual suspects have now been rounded up by Egyptian authorities. What happens next is anyone's guess. But, if you are a Coptic Christian, I suggest you get out. Now.