As in several previous shootings involving security companies affiliated with the State Department, witnesses to Saturday’s shooting said they saw no reason for the guards to open fire on the car, a white Hyundai with a taxi sign on the roof, driven by Mohamad Khalil Khudair, 40. It was unclear where the convoy was headed, or whether it carried any American officials.

“The poor cabdriver was stopped here,” said one witness, Raafat Jassim, 36, who said he was standing outside a barbershop near the exit ramp at the time. “He had his hazard lights flashing, and the convoy was a long way away from him,” Mr. Jassim said, pointing to a spot about 50 yards down the ramp, which comes off a bridge over the Tigris River in a neighborhood called Utafiya.

An official at the local police headquarters said that the victim’s brother had insisted on pressing charges against the company and that as a result, the case had been referred to an Iraqi judge. But legal loopholes and immunities in Iraqi and American law have raised questions about whether private security companies operating in this country can be called to account in any court.

Both the State Department and DynCorp confirmed that there had been a shooting involving one of the company’s convoys on Saturday. Possibly because the convoy sped away after the shooting, neither the company nor the State Department could immediately confirm that Mr. Khudair had been killed.

But Gregory Lagana, a DynCorp spokesman, said the details of the encounter in which Mr. Khudair died appeared to match the one in which DynCorp guards reported discharging a weapon on Saturday. “We’re assuming it’s the same incident,” he said.

Image Raafat Jassim, a witness, said the cabdriver had his hazard lights flashing, and the convoy was a long way away from him. Credit... Joao Silva for The New York Times

“We’ve stood down that particular team,” Mr. Lagana said, pending an investigation. “We take this kind of thing very seriously.”