I have been through the shower pics numerous times now, and I really think he wasn't posing, and she was taking those without his knowledge. I've studied the close up face shot, and especially the eyes, and he still looks frightened or startled to me. It's odd that she only turned the flash on for the last two pictures, the face shot and the shot of his lower body sitting in the shower. I also think the shower door was still closed in the face shot. The water seems to be running down the door as well as his face. But the door appears to be open in the shot of his lower body seated in the shower. There isn't the same water running down the door effect in that shot. Creepy.
I think he opened the door (like WTH), she snapped the lower body shot by accident (or on purpose), went to toss the camera (depressing the button once more that took the shot of the ceiling), and attacked him with the knife she was holding in her other hand. It's a small camera. She could definitely hold it in one hand and snap the pics. I tried it, and I have small hands. Does anyone remember if the ME said the wounds were right or left angled? (Sorry information overload, and I don't have time to go back to the ME testimony.) She appears to be left handed, so I wonder if she had the camera in the right hand (right handed camera) and the knife in the left, which would be her dominant hand.
I don't think those are scratch marks on his back - too patchy to be cat scratches. I think he had a lot of freckles and moles and that, along with the water running down his back, it somewhat gives the impression of lines.
It would not be that hard to sneak up on him showering if she had a zoom lens. And she could stash those weapons anywhere in the bathroom that was convenient to her, or even on herself if she were fully dressed. All MOO.