TRACY, Calif. – The Iraqi government has arrested one of two Iraqi troops accused of killing two American soldiers while the Americans were training them, a senior military official said yesterday.

The June 2004 deaths of Army Specialist Patrick McCaffrey Sr., 34, of Tracy, and 2nd Lieutenant Andre Tyson, 33, of Riverside, originally were attributed to an ambush during a patrol near Balad, Iraq, but the Army this week said a military investigation found the two had been shot to death by Iraqi civil defense officers.

It was unclear how long the Iraqi suspect has been in jail, said the military official, who spoke on condition of anonymity because the information had not yet been made public. The second trainee is believed to be dead, the official said.

A Pentagon spokesman said he knew of no other similar incident and called it “extremely rare.” An Army spokesman, Paul Boyce, said Tuesday that the Army had conducted an extensive investigation into the deaths, but declined to provide additional details.

The families of McCaffrey and Tyson, both California National Guardsmen, were being briefed on the report Tuesday and yesterday by Brigadier General Oscar Hilman, the soldiers’ commander at the time, and three other officers.

Soldiers who witnessed the attack have told Nadia McCaffrey that two Iraqi patrolmen opened fire on her son’s unit. The witnesses also said a third gunman simultaneously drove up to the American unit in a van, climbed onto the vehicle, and fired at the Americans, she said.