Lantar Sidonis

Lantar Sidonis is a turian, against whom Garrus Vakarian holds a grudge. Prior to Garrus's role as "Archangel," Sidonis was one of Garrus's squad mates in the Terminus Systems. Sidonis sells information regarding the squad's location to various mercenary groups, while giving Garrus a false lead. By the time Garrus spotted his dead teammates, Sidonis had already vanished, with Harkin having facilitated his disappearance. During Mass Effect 2, Commander Shepard and Garrus eventually learn of Harkin's role with Sidonis. After interrogating Harkin, a meeting between Shepard and Sidonis is set up while Garrus sets up a sniping position to assassinate Sidonis. Shepard has the choice to facilitate Garrus's assassination by leading Sidonis into Garrus's line of sight or warn Sidonis of his assassination attempt.

If Shepard chose to do the latter, it is revealed that Sidonis was under duress by the mercenary syndicates and only sold out the information to save his own life. As a result, Sidonis had suffered from survivor's guilt, eventually apologizing to Garrus via Shepard's communicator, and mentioning that "he'll make it up to him somehow." It's later revealed in a news report on the Citadel that Sidonis turned himself in to C-Sec, confessing to the murders of Garrus' team. However, it is uncertain if he will be convicted, as the murders were committed on Omega and outside the Council's jurisdiction.

If Shepard helps Garrus, then Garrus will shoot Sidonis with a sniper rifle, killing him.

Garrus will become loyal regardless of the choice Shepard makes.