The death of Nicola Calipari by U.S. gunfire strained relations between Italy and the United States.
The agent was heading by car to Baghdad airport on March 4, 2005, shortly after securing the release of an Italian journalist who had been kidnapped in the Iraqi capital when he was shot at the checkpoint.
Another agent, who was driving the car, and the journalist, Giuliana Sgrena, were wounded.
U.S. authorities have said the vehicle was traveling fast, alarming soldiers, who feared an insurgent attack.
Italian officials claimed the car was traveling at normal speed and blamed U.S. military for failing to signal there was a checkpoint.