Chicogirl, yes, apparently she was wearing sweatpants. I also wonder about auto-erotic asphyxiation and if this was what happened. But considering she was wearing her sweatpants, it seems less likely in my mind. I am inclined to think that for whatever reason, James was seething mad that night. I tend to think he strangled Erin in a rage, not premeditated. He probably freaked out afterwards and called out to Erins's parents.... I can't really believe any other scenario. I have no idea what his motive was without knowing more about his personality and their relationship.
I agree with Bumblebug though, the police have done a very shoddy job. To not take DNA from Erin is unbelievable.