ROME – Italian investigators blamed American military authorities for failing to signal there was a checkpoint ahead on the Baghdad road where American soldiers killed an Italian agent, and concluded that stress, inexperience, and fatigue played a role in the shooting, according to a report released yesterday.

The probe found no evidence that the March 4 killing of intelligence agent Nicola Calipari was deliberate.

The Italians challenged the American contentions that the car was traveling at a speed of more than 50 mph, saying it was going half that speed. But, despite their refusal to sign off on the American report that the soldiers bore no blame for the death, the Italian investigators didn’t object to many of the American findings of fact.

Calipari was killed just after he secured the release of an Italian journalist, Giuliana Sgrena, from Iraqi militants who held her hostage for a month. American soldiers fired on the Italians’ vehicle as it approached the checkpoint near Baghdad’s airport. Ms. Sgrena and another Italian agent were wounded.

“It is likely that the state of tension stemming from the conditions of time, circumstances, and place, as well as possibly some degree of inexperience and stress might have led some soldiers to instinctive and little-controlled reactions,” said Italy’s report.

American investigators, in their report made public Saturday, said the American soldiers gave adequate warning, beaming a light and firing warning shots, as the car traveled toward Baghdad’s airport. They cleared the soldiers of any wrongdoing, sparking outrage in Italy, where Calipari had been hailed as a hero.