"When Sunni refugees from Fallujah settled in west Baghdad's Sunni strongholds such as Ghazaliya, al-Amriya and Khadhra, the first Shiiite families began to get threats to leave."
Read between the lines when they talk about "fighters". It was like I said Zarqawi struck the Shia before Fallujah, that mostly stopped when he had a base in Fallujah when it was gone the suicide attacks on Shia started again and al-Qaeda fighters after fleeing Fallujah in early 2005 went to Baghdad and started killing Shia. But, the Badr didn't get into it and this didn't become widespread until late 2005.
However, the Madhi Army didn't get into it until early 2006.
Shirley you jest! :)
Sadr and the Madhi Army in cohots with Iran.
Al Queda, terrorists in cohots with Iran.
Reports of sectarian killings started being reported right after the capture and incarceration of Saddam.