From Halopedia, the Halo wiki
Prior to being traumatized by the Flood infection of his Marine unit, this Marine was part of a Marine squad composed of Privates Bisenti and Mendoza, and PFC Wallace A. Jenkins and led by Staff Sergeant Avery Johnson. The squad was deployed into a swamp in search of a weapons cache under the control of the Covenant, later revealed to be a Flood containment facility. Once inside the facility, the squad met up with Captain Jacob Keyes, along with Privates Kappus and Riley and ventured further into the facility. After entering a large hall, the squad was ambushed and attacked by a wave of Pod infectors. The Marine escaped the Flood infection by playing dead, though he also witnessed the death of almost his entire squad. Shortly after the ambush, he fled and hid away from the Flood.
John-117 encountered the Marine in the facility while in search of Captain Keyes. John quickly disarmed the Marine after the Marine, now in a fear-crazed state, fired his M6D pistol at the sight of the Chief. The Spartan tried to comfort the Marine and urged him to return to the surface, but the Marine ignored him and crawled into a fetal position, whimpered, and then fell silent. The Marine then proceeded to shoot himself after John continued his search for Captain Keyes.
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