If you're looking for a similar quote to Syrus, you need look no further than Claudius, the new King of Denmark, crowned because he murdered his own brother. Claudius mentions several times that the guilt is weighing on him. Each time has an impact on the tone of the play as a whole. Here are two examples:
1. When Claudius and Polonius are preparing to spy on Hamlet to see what ails him, Claudius begins to let his guilt shine through. He says:
How smart a lash that speech doth give my conscience!
the harlot's cheek, beautied with plast'ring art,
is not mre ugly to the thing that helps it
than is my deed to my most painted word:
O heavy burthen! (III.i)
Here, Claudius's "painted words" are the lies and deceit that he continues to portray to his family and advisers. He feels guilty over his heavy burden.
2. When Claudius is praying for forgiveness in the confessional, he begins by saying "O, my offence is rank, it smells to heaven" (III.iii) and goes on to illustrate how he can't truly be remorseful since he still has all that he killed his brother for: "My crown, mine own ambition, and my queen" (III.iii). His guilt won't let him live his life and ultimately serves as his downfall at the end of the play.
To relate these two quotes to Syrus, Claudius never feels secure after murdering his brother. He knows that someone, most likely Hamlet, will figure it out and that he will be caught.