Othello himself is responsible for Desdemona's death. It was a case of premeditated murder. Iago made Othello suspicious and jealous, but there is no proof that he even intended to provoke Othello into killing his wife. It could be argued that Iago, because of his hatred, wanted to spoil Othello's happiness but not that he expected Othello to go so far as to commit a murder. Othello himself seems to be considering an alternative way of dealing with Desdemona in his soliloquy. The logical thing to do would be to seek a divorce or an annulment, yet Othello in his soliloquy beginning, "It is the cause, it is the cause, my soul" says "Yet she must die, else she'll betray more men." (V.2)
He is rationalizing here. He is not concerned about other men she might betray but about setting her free to have intimate relations with other men. He wants to keep sole poasession of her even after her death. His love and his jealousy are both so strong that he loves her while he is strangling her. That is the poignant climax to the play: a man kills the thing he loves best in the world. Shakespeare wanted to make this internal conflict clear.
Ultimately, Othello is responsible for the death of Desdemona. For to quote Saint-Exupery (author of The Little Prince): "To be man is to be responsible." That is, each person must be responsible for his own actions.
Nevertheless, the question of Othello's guilt is not a simple one. For he has been victimized at the hands of a foreign culture, and he also has a propensity to torment himself, as well as possessing a vulnerability since he finds himself heroically reflected in Desdemona, a reflection that certainly leads to his tragic end. So, unfortunately, in murdering Desdemona, Othello acts in character. Underscoring this idea, renowned Shakespearean critic Harold Bloom terms Othello a hero-victim, a leader who is radically flawed. Bloom contends,
Othello sees the world as a theater for his professional reputation; this most valiant of soldiers has no fear of literal death-in-battle, which only would enhance his glory. But to be cuckolded by his own wife, and with his subordinate Cassio as the other offender, would be a greater, metaphorical death-in-life, for his reputation would not survive it, particularly in his own view of his mythic renown (William Shakespeare's Othello. New York: Chelsea House, 1987).
Thus, Bloom contends that because Othello perceives himself as an almost mythic hero, he views himself as a living legend who must not allow anyone or anything to undermine this perception. Indeed, Othello is the victim of his perceptions and his pride, a pride that drives him to murder the woman he loves as well as to murder himself. The blame for the murder of Desdemona must, therefore, fall upon Othello.