Theory on why the door was left unlocked...

I see people on the fence about if he did it intentionally - knowing he couldn't keep Jocelyn from finding out the truth for much longer - or if he just slipped up for the first time in eleven years. I personally believe he was delusional enough to think Amanda wouldn't try to leave.

I've followed this story since it first happened, taking an interest especially because Cleveland is so close to where I live. When he was in jail, I remember Amanda attended a concert with her sister and a male friend, who was hugging her and sticking close to her side when they were invited up on stage. I remember Castro released a statement through his lawyers saying how she didn't act like a kidnapped victim. I forget what all the statement said, but I remember thinking how absolutely jealous he sounded about the footage he had either seen or been told about. One of the times he was in front of the judge, he was even ballsy enough to ask when he could see Jocelyn. And (I believe in the People magazine interview) Amanda said how Castro told her that if she were to ever write a book, that she should tell the "truth" and admit that she had feelings for him in return.

In the movie it shows that Amanda was the most willing to go along with what he said, for fear of getting in trouble. She wouldn't even talk to Michelle through the door. In their book, she says she did a lot of things to appease him to stay on his good side. I think Castro was delusional enough to mistake this for affection. Amanda was clearly his favorite, and along with sharing a child together, I think he thought she might be the least likely to escape. That she had it "good" there, compared to the other two. Maybe leaving the door unlocked was a test; one not as severe as the tests he gave Michelle, because perhaps he believed Amanda really wouldn't leave. He might have started to get a little too confident, and thought he had her conditioned enough by that time. Why was her bedroom unlocked? And the door to boot? The screen was locked, but he might have left that just as a precaution, thinking if she did try something, that would deter her from going any further. That might not have even been the first time he left the door unlocked, it might have just been the first time it caught Jocelyn's attention.