That's a good question, because to my knowledge Christians have not contributed to the violence. As I think I mentioned, the church in Tahrir Square, one of the main churches, was open to act as an infirmary over these last five days of rioting that took place. Doctors were housed there.
Certainly during the Tahrir Square riots in January, the Christians initiated the period of time when they surrounded the Muslims while they were engaged in prayer for their protection, and then the Muslims reciprocated. The Christian churches in Tahrir Square also opened so that the Muslims could perform ablutions, ceremonial washing, prior to their times of prayer.