ROME -- Dissatisfied with the results of a joint investigation with the United States, Italy on Wednesday began its own probe into the March 4 killing of one of its intelligence agents by U.S. troops in Baghdad.

Italian officials said Rome prosecutors were looking for evidence of homicide in the case of Nicola Calipari, who was transporting a rescued Italian hostage to the Baghdad airport when U.S. soldiers opened fire on their car. The bullet-scarred Toyota Corolla was brought to Rome on Tuesday.

The prosecutors have demanded the names of the soldiers who were involved, but the Pentagon has denied the request, Italian officials said.

The Italian move follows the release this week of partial findings from the joint American-Italian investigation. The Americans concluded that their soldiers were not at fault and had observed the proper rules of engagement for firing at a suspicious vehicle, according to unnamed Pentagon officials. Two Italian investigators who took part in the probe have so far refused to sign on to the findings.

The controversy represents an unusual break between the Bush administration and Italian Prime Minister Silvio Berlusconi, whose chief aide, Gianni Letta, met with U.S. Ambassador Mel Sembler twice on Tuesday. Berlusconi has been one of Bush's most staunch European allies in Iraq, where Italy maintains about 3,000 troops.

The killing of Calipari, who had aided in the release of journalist Giuliana Sgrena from kidnappers, shocked Italians. According to an account from Sgrena, who was wounded in the shooting, Calipari threw his body over hers to protect her from the hail of bullets.

U.S. officials have said, however, that Calipari was partly at fault because he was traveling on a dangerous road at night and, they say, had not properly notified American officials of his plans.

The dispute has put at stake the reputation of a man viewed here as a gallant hero. "The government of Italy does not want a fight with the U.S.A., but it can't commit suicide by putting full blame on a national hero," commentator Alessandro Politi wrote in Il Messaggero, a newspaper in Rome.

The first findings from Italian investigators on Wednesday absolved Calipari of any "errors," an Italian official said.

Italian investigators who are examining the car are trying to ascertain how many bullets struck it and from which direction. "The important thing is not what Calipari did but what the people who shot him did," the official said.

Berlusconi had asked the United States for an admission of error but did not receive one. U.S. officials have contended from the beginning that, at most, the shooting was a tragic accident.

The Italian government has avoided detailing just how Sgrena's release came about. Stories of a ransom payment abounded in the Italian press at the time, and some commentators have questioned the wisdom of rushing Sgrena to the airport. "In almost two months from that tragic night, we have not grasped an ounce of truth or fact," Giuseppe d'Avanzo wrote in La Repubblica, a newspaper that has been highly critical of Berlusconi.

"It looks as if the love affair is over between Bush and Berlusconi," an Italian Foreign Ministry official said. "Berlusconi needed help, and the administration did not supply it. The Americans were not going to sacrifice the morale of their soldiers for Berlusconi." Shortly after the shooting, Berlusconi announced that he would begin to withdraw Italy's troops from Iraq in September.

Berlusconi's popularity has plummeted in recent months, largely because of inflation and stagnation in the national economy. The Baghdad shooting took place about six weeks before regional government elections in which Berlusconi's coalition fared poorly.

It is not clear whether Calipari's death contributed to Berlusconi's woes, but commentators have been quick to point out that the prime minister's closeness to Bush has all but lost its political usefulness. This week, Berlusconi reconfigured his cabinet to try to keep his coalition afloat and avoid early national elections.