Chet Tyber was the head of security at a Marine base in Afghanistan, as well as a former special ops soldier with Sniper training.
Prior to being deployed as the civilian head of security for the Marine base at Afghanistan, he acted as a marksman member of the special forces, where he had training as a sniper and graduated at the top of the class. He and his civilian contractor partner proceeded to retrieve valuables from various homes that were initially rigged with IEDs when cleared out. Ted Lemere uncovered this and refused the offer when asked by his partner. Tyber himself, however, did not want to take any chances, and plotted to murder him via a sniper round, and trick his partner into thinking Taliban insurgents were responsible for Lemere's death via the echo of the shot. He then proceeded to shoot the official suspect when they targeted him, although even he was unsure whether his was the shot that brought him down. Lemere, however, suspected he might end up being killed for his discovery, and informed his wife as much in what was ultimately his last video call to her, getting NCIS involved. His involvement was eventually uncovered, and he attempted to shoot Gibbs (himself a former sniper), but Dex, Lemere's assigned bomb-sniffing dog, pounced Tyber and was brought down by the shot, although he ended up shot in the shoulder by Gibbs shortly thereafter. He was presumably arrested shortly thereafter.
His accent implies that he may have originally lived in Austria.