I'm not here to argue with ya Rob, but IMO...
Everything is hear-say. And everyone HAS a choice when doing something "stupid". You either do the right thing, or you do the wrong thing. Craig and Kelly did the wrong thing...several times. They beat this woman, they tazered this woman, they shot her up with drugs, they choked this woman, they tied this woman up, they put this woman in a trunk of Kelly's car, they burned this woman in this car and they ran from the police. According to you, their motive was...they did so because she stole Kelly's identy and shopped til she dropped. I'm only asking, so don't jump all over me, but where did this story come from? Where is the proof? Who was it that claimed Melissa stole Kelly's identity?
Obviously someone has to be pretty pissed to be so violent on another human being, so I am going to presume Melissa did piss either Craig or Kelly off, but if it were true that Melissa was stealing Kelly's identity and stealing their money...wouldn't you go to the police? Uusally only HUGE drug dealers and "mafia" type people go and murder someone for such....and they pretty much know how to "dispose" of a body without it ever being found. People who kill in the heat of the moment (and kill usually for stupid reasons or by accident) are "sloppy" about the murder and getting rid of the body.
There are so many stories and ideas on the motive (I read that Kelly was pissed that Melissa and Craig were carrying on in an affair and approached Melissa about it and a fight broke out between the two and Kelly tazered Melissa. Fearing she did in fact kill her, she shot her up with enough drugs to make it look like an od. Craig came in after the fact and did what he had to to protect Kelly, etc.) that it could be anything.
These people (all involved) were obviously not playing with a full deck and like I said, we (the public) might never really know what happened and why...hence (IMO) Bob's quote stating "stupidity was the motive".