In Othello, who is responsible for Desdemona's death?

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-

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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.