According to some of the commenters at youtube, during the uprisings the Egyptian police told the monastery they would no longer be able to protect them. The Coptics were told they would have to protect themselves. In order to do that, the Copts built a wall in front of their monastery to protect it. The Egyptian army claimed the wall was built without government permission, so they came with tanks to knock it down. When the unarmed Copts objected, the Egyptian army opened fire on them. This monastery has been there since the 5th century AD.
This is just so tragic.