'To confess, and be hanged for his labour! First to be hanged, and then to confess: I tremble at it.' Can somebody explain these lines to me?...

These lines come from Shakespeare's,
Othello, Act 4. Scene 1. They are spoken by Othello who is in a
rage. During his discussion with Iago,the villain of the play, he is unwittingly
covinced that his wife, Desdemona, is having an affair with Cassio, his lieutenant. When
he says, "To confess, and be hanged for his labour! First to be hanged, and then to
confess: I tremble at it," he means he will murder Cassio first and then give him a
chance to confess. In other words, he will kill him and cares not to give him the
slightest benefit of the doubt since his supposed action of adultery is one of grave
betrayal. Othello is so enraged, he is shaking due to adrenalin coursing through his
veins.