In act 5, scene 1 Iago and Roderigo had wanted to kill Cassio. Basically i guess if cassio had lived through all the supposed "killing" Iago was going to ransom. Cassio had almost been stabbed by Roderigo. Roderigo used self defense and hit him back. Then Cassio called for help. Lodovico and Grantiano had stepped in to his rescue, aswell as Bianca. Iago ended up lying about the story. Roderigo whom died, while Iago continues to lie.