
Other mistake: After Dan visits his wife in the hospital, he goes to Alex's apartment. In the scene where he's chasing Alex and crashes into the glass door, shattering it, look closely at his face and you'll see it's not Michael Douglas but a stunt double. A few seconds later when they are struggling in the kitchen, look again and you'll see the same stunt double.
Answer: Because she is insane! And she picked the lock. By murdering the innocent pet bunny rabbit Alex was sending a message. She won't be ignored! She's just letting Dan know that she can get to him, or in this case his family (daughter's pet), anytime she wants to. He's not safe.
Alan Keddie