They have DNA from her body fluids found on the inside of his trunk. They have his lies to police. He's going down for murder, imo.
IMO, they need a body before he goes down for murder. I've follwed numerous cases where LE charged someone with murder with no body based on blood evidence and such, which tells me they don't have that. Unless they find Christina or he confesses, tthey don't have enough for murder.