"I get nightmares," Lozano told CBS News chief foreign correspondent Lara Logan. "I think about that guy."
He says had no idea who was inside the car that came speeding towards his unit after curfew, so he flashed a warning light.
"Iraqi civilians, when they see the light — that big spotlight — that means stop," Lozano said.
But he says the car carrying agent Nicola Calipari and the Italian hostage he had just freed — kept going.
"As soon as I see the vehicle maintain that speed, I knew he wasn't going to stop," he said.
What was going through his mind at that point when he saw the car coming at him?
"My daughters," Lozano said. "I mean, my daughters is like No. 1 in my life, you know. And I just don't want them to grow up without a kid, you know, without a father."
So Lozano said he fired a warning shot.
"The car still didn't stop," he said. "So, I just, I just had to shoot at the car. I had no choice."
Lozano's bullets killed Calipari and wounded journalist Giuliana Sgrena who had just survived 28 days as a hostage. After the incident, he was silenced by the military — but she told the world U.S. soldiers deliberately tried to kill her.
"So when the Italian journalist said there was no light flashed, that's not true?" Logan asked.
"It's not true," Lozano said.
"When she says there's no warning shots, is that true?" Logan asked.
"There was warning shots," Lozano said. "It's not true."
"When she says the vehicle was fired upon 3 to 400 times, is that true?" Logan asked.
"No, that's a lie," Lozano said. "Because in order for that to happen I would have had to reload."
Those details have never been heard in Italy where thousands poured onto the streets to mourn their national hero. His death enraged a nation already turning against an unpopular war.
"I felt like I hurt one of my own soldiers," Lozano said. "It's a terrible feeling you know. I wouldn't with that on anybody, on any soldier."
Dan O'Shea, a Navy SEAL and head of Iraq's Hostage Working Group at the time, says what happened is not Lozano's fault.
"He was doing what he was trained to do and he needs to be defended for that," O'Shea said.
He believes the Italians didn't want their U.S.-ally to know they'd paid a ransom to the hostage takers, and that Nicola Calipari himself ordered no one should be told of the trip to the airport.
"He's got no one to blame for his death, unfortunately, other than himself," O'Shea said of Calipari.
But it's Mario Lozano who is being tried for murder in Italy. CK HERE UNCLEAR.
"In your mind, in your conscience, are you clear of any wrongdoing?" Logan asked.
"Yes," Lozano said. "I'm just an infantry soldier, doing my job, you know."
"If you were talking to his sons and family right now, what would you say to them?" Logan asked.
"Well, that's tough. I wouldn't know what I'd say right now. I don't even know if I could look at them in the face, really, you know," Lozano said. "Not because I feel like I did anything wrong. Just because I know the grief they might have gone through."
That's a burden Mario Lazano says he will carry for the rest of his life.