Among the mourners on Monday was Prime Minister Silvio Berlusconi, who sent Nicola Calipari on his fatal mission to Baghdad and is struggling to reconcile his fervent pro-US policies with demands for the truth from Washington over the shooting.
Hundreds of Italians lined the streets as Calipari's body was driven to the basilica of Saint Mary of the Angels and Martyrs for the funeral, which was shown live on television.
Uniformed soldiers provided a guard of honour and crowds broke into applause as the coffin, draped in the Italian flag, was carried aloft into the crowded church.
In the line of fire
"It is time to honour the heroic sacrifice of Nicola Calipari, without divisions, all together, without controversy. Let's leave the controversy outside," top government official Gianni Letta said in an address, fighting back his tears.
Calipari died from a bullet to the head as he threw himself over journalist Giuliana Sgrena when US forces opened fire on their vehicle just outside Baghdad airport on Friday.
Giuliana Sgrena was wounded when
US forces fired on her vehicle
Sgrena, who had been freed minutes earlier by her Iraqi captors after a month in captivity, is recovering in a Rome hospital from a bullet wound to the shoulder.
Sgrena and an Italian secret service agent driving the car have denied US assertions that soldiers only fired on them after they had failed to heed signals to slow down and also rejected claims that they had been speeding.
Sgrena, who writes for the newspaper Il Manifesto, has suggested they were targeted because the United States opposes Italy's practice of negotiating with hostage-takers.
"Unfortunately only the Americans know what really happened. I hope eventually we will find out the truth"
The Italian government has made clear that it will continue to support US President George Bush despite the killing and will not withdraw its troops from Iraq. But at the same time it is demanding those responsible for the shooting be punished.
"The alliance with the United States is not up for debate, likewise our military commitment to Iraq," Berlusconi was quoted as saying by Italian newspapers on Monday.
Nonetheless, there was anger across Italy, with politicians of all colours rejecting the official US explanation.
"Unfortunately only the Americans know what really happened. I hope eventually we will find out the truth," said Sergio Mandoza, one of an estimated 100,000 people who filed past Calipari's coffin over the past 24 hours as it lay in state.
Calipari worked out of Berlusconi's office and was a highly experienced hostage negotiator who had secured the release of two Italian aid workers taken captive in Iraq last year.
But his killing has cast a spotlight on widespread speculation that Italy is paying off hostage-takers.
Although the government denies paying ransoms, officials say off the record that money was paid to win Sgrena's freedom, with sums of $6 million to $8 million being mentioned in the press.
The United States and Britain, which have the biggest military contingents in Iraq, condemn such payments, arguing that they fuel the hostage trade.
Bush has promised Berlusconi, one of his closest allies in Europe, a full investigation into Calipari's death. The Italian prime minister is hoping for answers before he addresses parliament on Wednesday over the shooting.
In previous "friendly-fire" deaths, the Pentagon has not publicly admitted to any culpability on the part of US forces.
"What has happened cannot be used as an alibi to revive anti-Americanism"
Pier Ferdinando Casini,
speaker of the lower house of parliament
Italian officials have rejected Sgrena's claim that she might have been deliberately shot at, but they fear any hint of a US whitewash will inflame anti-American sentiment in Italy.
"What has happened cannot be used as an alibi to revive anti-Americanism," said the powerful speaker of the lower house of parliament, Pier Ferdinando Casini.
"(But) friendship can never be servitude and for this reason we have to ask with determination to have the truth and clarity," he told La Repubblica newspaper in an interview.