From Wiki:

After the re-ignition of the Fatah-Hamas conflict on June 10, Hamas militants seized several Fatah members and threw one of them, Mohammed Sweirki, an officer in the elite Palestinian Presidential Guard, off the top of the tallest building in Gaza, a 15-story apartment building. In retaliation, Fatah militants attacked and killed the imam of the city's largest mosque, Mohammed al-Rifati. They also opened fire on the home of Prime Minister Ismail Haniya. Just before midnight, a Hamas militant was thrown off a 12-story building.