MM's long time friend said he was into the occult and demonic worship. Police found lots of books on this subject when they raided the apt. I think this was some type of demonic ritual they performed on Bella sacrificing a child. The abuse, torture, rape is a way to gain mind control with this cult according to books on this subject. That's why they put her in the refrigerator to preserve her body to eat later as this is what devil worshippers do but perhaps changed their mind. Read about it. If he worships the devil why would he kill her if "possessed by devil" this doesn't make since he worships the devil. I believe they were both part of this and had agreed they would tell everyone she was with DCF. They knew people would believe the story since the other two were taken away. They would have been smarter to say she was kidnapped. It would have been harder to prove like Casey Anthony story.
I think she got mad at MM no longer wanted him and decided to push him to the curb to start a relationship with JA again. She wanted him back but knew she would have to come up with a story because he would eventually find out about Bella not being with DCF so she would create a story to blame it all on MM so she wouldn't be the killer. That's why JA said he was looking forward to being a family again. Him, RB, and Bella.
I believe this is why MM was shaking his head in court and stuck with DCF story as that was what both of them agreed to do after they killed Bella in a demonic sacrifice ritual they did when high. Since he was into that crap. I'm sure RB went along with it.
http://www.whale.to/b/sullivan.html