I think he was charged with first degree murder because of the surrounding circumstances she was found in a suitcase in the trash until that have completed their investigation and have ME reports etc. this way he's kept behind bars without bail.
In CA first degree means it was premeditated or planned. Lying in wait could be a death penalty case. I really don't feel this monster planned it or he would have done a much better job of hiding her body. I'm sure both were highly intoxicated from drinking which escalates tempers and jealousy. He's probably a woman abuser and has anger management issues.
I'm sure they had a dysfunctional relationship. Drinking and fighting don't mix especially if you throw drugs in the mix. I have a feeling he strangled her which a defense attorney would probably go for a 2nd degree. Heat of passion. They will probably get a mental evaluation and this will drag on and on for a few years since CA unless he takes a guilty plea agreement which I highly doubt. He comes across as being narcissistic from people that knew him.
She must have been a tiny little girl to have fit in that suitcase. If rig had set in it would not have been easy to unfold her. It makes me sick thinking about this. Poor girl. RIP Shauna
http://statelaws.findlaw.com/california-law/california-first-degree-murder-laws.html