I'm still undecided as to whether he knew she was armed or not; his expression doesn't seem particularly worried in any of the pics that she may do something nuts, but he also doesn't appear to be enjoying himself or striking poses for the camera.
Since he was modest and even she admitted (to Flores) that he wouldn't willingly submit to a nude photo shoot in the shower, she obviously coerced him somehow, but I'm not sure it was with a weapon. He does seem to know near the last couple that it's not going to end well, but even in the full face shot I don't see outright fear. In that one he wasn't even looking at her face, the camera flash is on his upper forehead and his line of sight is below it. Just something I noticed. lol