Cassio is innocent. He was true and dedicated to Othello.. He went to Desdemona to ask for her help him get back in Othello's good graces. Iago manipulated Othello's insecurity about being old, a Moor and unsophisticated into a jealous rage. He took every opportunity to insinuate Cassio and Desdemona were sleeping together.
Iago fabricated a story about when he and Cardio shared a bed . He said cassio called Desdemona in his sleep, wrung his hand, and kissed him on the mouth, then threw his leg over him.
Iago used the scarf Desdemona dropped while fighting with her husband about wrapping his head to relieve a headache to set her up.
