JMO~
I believe that Sam was looking for Theresa that Wed. night when a call was placed to her sisters (Christina) house at 10:44. He couldn't confront her at her new apartment because he didn't know where it was. I believe he was angry because she was moving on with her life and he waited on her to get home that night. Theresa was probably looking forward to the next few days of moving into her new place. Sam was furious he had no more control over her life, and had one last opportunity to confront her when she returned home that night. If he strangled her he wouldn't have to worry about any blood, and hid her body somewhere. Then, he makes sure he has a solid alibi for Thursday. GBI knows though she went missing Wed. night. All of this is JMHO!!