Complex sentence: Brian begins investigating Hector and Tran's activities and is convinced that Tran is behind the hijackings, believing his suspicions are founded when he discovers an unusual purchase made by Hector in The Racer's Edge (the parts shop where Brian works).
Split into simpler sentences: Brian begins investigating Hector and Tran's activities and is convinced that Tran is behind the hijackings. He believes his suspicions are founded when he discovers an unusual purchase made by Hector in Racers' Edge (the parts shop where Brian works).