Iraqi Shia police death squads.

According to this report, Iraqi Army troops arrested 22 "highway police officers, wearing police commando uniforms" in January 2006. The arrestees freely admitted they were taking a Sunni man away to be shot:

To complicate matters, the four men at Abu Ghraib were named as members of the Badr Brigade, the armed militia of the Supreme Council for the Islamic Revolution in Iraq, the Shia political party that heads the interior ministry and will conduct the inquiry.

Which is to say, this is an instance of extrajudicial killing that is not going to convince the Sunni minority in Iraq that the cops are to be trusted.

The temptation on the part of the Shia to take revenge on the Sunnis who so creatively killed and tortured them is understandable but must be resisted. If indulged, all Iraq will enjoy will be interminable civil war. The Sunnis who (with their Saudi, Egyptian, Afghan, Syrian, and Iranian compatriots) are mounting a creditable defense against American and Iraqi troops are capable of making life miserable for the Shia should they attempt to take control.

Sheikh Muqtada al-Sadr.

The X Factor in this incident is the obvious connection between the Badr Brigade, and this delightful man, who has ties to Iran and is nothing but an ambitious politician and militia commander masquerading as an imam.

"Iraq police death squad arrested at checkpoint."
Oliver Poole, Telegraph, 2/17/06.