I think he's going to plead self-defense, panicked and hid the body. Otherwise he's going to either plead guilty or mental defect, insanity. The evidence seems to be too damning to try to say he had nothing at all to do with her death.
I agree. I think he'll say that they had a verbal confrontation that got physical and then went horribly wrong. And then he freaked out and hid the body.