Why does Iago stab Roderigo at the end and why does he pretend to Lodovico that he does not know what is happening?

Roderigo knows what Iago has been up to..... his lies and manipulation...... the actions that were responsible for suspicion, deaths, and suicide. Thus, Iago needed him out of the way. Iago feigns innocence with Lodovico for the same reason.