Desdemona is killed by her husband, Othello. He smothers her in the belief that she has been unfaithful to him with a Cassio, a member of Othello's staff. Desdemona tells us of her innocence in Act V Scene ii-
O, falsely, falsely murdered!
And indeed Othello confesses to his crime-
She's like a liar gone to burning hell;
'Twas I that kill'd her.
However, it is through the cruel machinatios of Othello's ensign, Iago, that Othello has believed the tale that Desdemona was unfaithful. Once Emilia is able to piece together Iago's wicked plot, she directs the guilt squarely at her husband -
And your reports have set the murder on.
In the final lines of the play it is clear whom Lodovico, as representative of the Venetian government, believes is responsible for the tragedy which has befallen as he addresses Iago-
O Spartan dog;
More fell than anguish, hunger, or the sea!
Look on the tragic loading of this bed;
This is thy work.