From Halopedia, the Halo wiki
In 2527, washed-out Spartan-II Soren-066 was assigned to a desk job in Partch's department. Six months later, Partch began talking to the young man about revolution. In his vulnerable state, Soren listened. Partch eventually brought Soren over to the side of the rebels by slowly feeding him ideas that the actions of the UNSC, well-intentioned though they may have been, were often wrong, and the Outer Colonies did in fact have a right to be independent.
Some time later, Partch decided that the time was right to openly defect to the Insurrectionist cause, but first he chose to take a "souvenir." Later that night he and Soren broke into a laboratory and stole a small titanium case. The two were interrupted by another Spartan, Randall, who was suspicious of their explanations for being there. As Randall led them out of the lab to confirm their story Soren attacked him, and as the two fought Partch shot Randall with a tranquilizer dart. Partch and Soren then fled the complex in an old C709 Longsword-class Interceptor which Partch had pre-prepared and hacked, complete with a "dumb" AI named Captain Teach whom he had fast-grafted to convert him over to their side. However as they attempted to flee Reach, the Longsword was pursued and damaged too severely to break the planet's gravity. As Soren attempted to crash-land the craft Partch passed out, either from fear or the g-forces of the fall, before waking again and screaming. Partch was killed when his neck broke during the crash landing. His body was found in the mangled wreckage, burned beyond recognition, although the UNSC was able to determine his identity by examining his DNA.
Chief Petty Officer Franklin Mendez stated afterward, "We don't know how that one got in here in the first place- take one look at his background and he has all the earmarks of a rebel." Mendez reasoned they had a problem with someone higher up in security.
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