KUWAIT CITY, Kuwait (AP) -- A military tribunal began hearings Monday for a U.S. Army sergeant charged with killing two superior officers in Iraq, with a witness testifying that the defendant told him he wanted to kill one of the victims.Staff Sgt. Alberto B. Martinez, of Troy, New York, faces murder charges in the June 7 killing of Capt. Philip Esposito and Lt. Louis E. Allen in a bomb blast at Forward Operating Base Danger, near the central Iraqi city of Tikrit, the hometown of the deposed Iraqi leader, Saddam Hussein, some 80 miles north of Baghdad.It is believed to be first case of an American soldier in Iraq accused of "fragging" his superiors. Fragging is a Vietnam War-era term used to refer to soldiers killing their superiors.The tribunal, held at Camp Arifjan in Kuwait, will determine whether to send the case to a court martial.During Monday's session, one witness, Capt. Carl Prober, said Martinez told him twice that he hated Esposito -- once in September 2004 and again in May. In the second instance, Martinez said "specifically I hate (Esposito) and I'm going to frag (him)," Prober testified.Prober did not say why Martinez said he hated Esposito.Esposito, 30, of Suffern, New York, and Allen, 34, of Milford, Pennsylvania, were killed by a blast in Esposito's office in a former Saddam palace being used as a base. Their deaths were initially thought to be a result of "indirect fire" on the base -- a mortar round that struck a window on the side of the building where Esposito and Allen were.Senior Master Sgt. Kevin Fitzgerald, an expert on explosives, testified that the blast was caused by a Claymore anti-personnel mine and possibly three grenades. Surgeon Col. Joan Sullivan told the tribunal that the men's injuries were not consistent with wounds caused by a mortar or rocket.Eight witnesses were heard in a morning session, and several more were to be heard in the afternoon. The hearings could last until Wednesday.The widows of Esposito and Allen attended the hearings after the Army agreed to fly them to Kuwait for the sessions.Martinez, 37, a supply specialist who joined the New York Army National Guard in December 1990, was deployed to Iraq sometime after October 2004 with the 42nd Infantry.The Tikrit case is the second known incident in which a U.S. soldier has been charged with killing his comrades during the Iraq war.In April, a sergeant in the Army's 101st Airborne Division was convicted of murder and attempted murder for a grenade and rifle attack that killed two officers and wounded 14 soldiers in Kuwait during the opening days of the 2003 invasion.Hasan Akbar, a 34-year-old Muslim who was sentenced to death, told investigators he staged the attack because he was upset that American troops would kill fellow Muslims.Fragging incidents also were reported during the Vietnam War, particularly in the late 1960s as the strains grew on a draftee army waging an unpopular war. Soldiers feeling hassled or unnecessarily put in harm's way by their commanders often settled their grievances with a fragmentation grenade.Between 1969 and 1971, the Army reported 600 fragging incidents that killed 82 Americans and injured 651. In 1971 alone, there were 1.8 fraggings for every 1,000 American soldiers serving in Vietnam.Copyright 2005 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.