McGuffin was a Comm Specialist onboard the TCS Concordia.
While the ship was in the Niven system during the Enigma Campaign, McGuffin had duty in the auxiliary Commo Room. He left the post to take a cup of coffee, allowing Major Zachary Colson in his stead. During his absence, Colson (who was actually a member of the Society of the Mandarins) used his console transmit data to a Kilrathi agent. McGuffin returned earlier than expected and saw the Kilrathi's face on the screen.
MacGuffin is a cinematic term of a plot device which motivates and advances the narration, while however it is not important to the narration itself. McGuffin is obviously a pun on this word: His background is not explored in the game's scenario, nor he plays a large part, however his murder motivated important events in the game.