I really think Surraya Committed Usman's Murder.
Usman found out her real intentions but did not say anything to her because after all its his wife. He quietly watched her each step and he knew she was up to something evil. Now that we know for sure Usman had his will changed without anyone knowing and everything went to Aliya and his last words were Aliya has something to do deeply with his past with Surraya.
Surraya can go to any extend to get what she wants. Her intentions were Money, Zaya's divorce whatever it may have been she got it even if it cost her Usman's Death she can not accept defeat.
But again- is stopped watching the show and read Written Updates or read news feed and got me to see what this mystery is.