On 20 January 2007, a group of gunmen attacked the Karbala Provincial Joint Coordination Center in Karbala, captured four American soldiers, and subsequently killed them. The attackers passed through an Iraqi checkpoint at around 5 pm, a total of five black GMC Suburbans, similar to those driven by U.S. security and diplomatic officials. They were also wearing American military uniforms and spoke fluent English. Because of the sophistication of the attack, some analysts have suggested that only a group like the Quds Force would be able to plan and carry out such an action. Former CIA officer Robert Baer also suggested that the five Americans were killed by the Quds Force in revenge for the Americans holding five Iranians since the 11 January raid in Irbil. It was reported that the U.S. military is investigating whether or not the attackers were trained by Iranian officials; however, no evidence besides the sophistication of the attack has yet been presented.