[JURIST] The US Army Thursday charged staff sergeant Alberto B. Martinez of the New York National Guard 42nd Infantry [official website] with the murders of his two commanding officers at an army base near Baghdad. An initial military investigation concluded that the officers were killed by a mortar round, but it was later ruled that the "blast pattern" at the scene of the crime was not consistent with a mortar attack. A military official said Martinez is believed to have used a device such as a grenade to carry out the premeditated attack. Read the US military press release on the charges. This is believed to be the second case during the Iraq conflict of a US soldier intentionally killing superiors - a practice that became known in the Vietnam war as "fragging" [MPs in Vietnam backgrounder] - and the first such case to take place in Iraq itself. In April 2005 Sgt. Hasan Akbar was sentenced to death [JURIST report] for a grenade attack that killed two officers and fourteen others at a US military base in Kuwait. AP has more.