Complex sentence: Sam assumes that he is there to prevent Lisa from ruining her career, and discourages her from telling anyone about the alibi, figuring that since he is only a minor suspect, he will find some other way to prove his innocence.
Split into simpler sentences: Sam assumes that he is there to prevent that, and discourages her from telling anyone about the alibi. He is confident he will find some other way to prove his innocence.