An Army staff sergeant has been charged with deliberately killing two officers whose deaths in Iraq last week were first reported to have been the result of an enemy mortar attack, the U.S. military announced yesterday.

Staff Sgt. Alberto B. Martinez, identified as a 37-year-old supply specialist with the 42nd Infantry Division, was charged with two counts of premeditated murder.

The officers killed were Martinez's company commander, Capt. Phillip T. Esposito, 30, of Suffern, N.Y., and the company's operations officer, 1st Lt. Louis E. Allen, 34, of Milford, Pa. On June 7, they had been conferring about the next day's missions in their headquarters building in Tikrit when an explosion occurred about 10 p.m., according to Army officials familiar with the case.

"The initial investigation by responders and military police indicated that a mortar round struck the window on the side of the building where Esposito and Allen were located at the time," said a statement issued late yesterday by the U.S. military command in Baghdad. "Upon further examination of the scene by explosive ordnance personnel, it was determined the blast pattern was inconsistent with a mortar attack."

Instead, investigators now say, the attack involved a mine or grenade or both.

Army spokesmen in Washington and Baghdad said they had no information on what may have motivated the attack. Martinez, whose home town is listed as Troy, N.Y., joined the 42nd Division -- a National Guard unit based in upstate New York -- 15 years ago.

The division took over responsibility for a large section of north-central Iraq in January. It is headquartered in Tikrit, home town of former Iraqi president Saddam Hussein, about 80 miles north of Baghdad.

Martinez, who was formally charged Wednesday, is being held at a military confinement facility in Kuwait and is represented by a military defense attorney, the Army statement said.

Initially, the U.S. military in a June 8 statement attributed the two officers' deaths to an "indirect fire" attack on Forward Operating Base Danger near Tikrit. "Indirect fire" generally refers to artillery or mortar rounds shot from some distance away.

Within a day, however, military investigators had changed their assessment, and the families of the dead officers were notified of the change last Thursday, according to Army officials.

A military statement last Friday, publicly disclosing the names of the dead officers, blamed the deaths on "an explosion of unknown origin." Yesterday's statement announcing the murder charge was not released until after funeral services for Allen in Goshen, N.Y., earlier in the day. Esposito was buried Wednesday in Nanuet, N.Y.

The case marks the second reported incident in the Iraq conflict in which a U.S. soldier has been charged with killing comrades. During the opening days of the invasion in March 2003, Sgt. Hasan Akbar of the 101st Airborne Division threw grenades into tents in Kuwait and fired on troops, killing two officers and wounding 14 soldiers. Convicted of murder in April, he has been sentenced to death.