The house was a decent size, but not huge. I would think in that house that she would've heard something also. Unless "downstairs" was the basement, then it would've been harder to hear. If he told her he was putting the kids to bed, she probably wouldn't have had anything on loud (tv, radio, etc.).
The neighbor that found Lauren said there were bad bruises on her forehead...........so I'm thinkin that when he tried to drown her in the toilet he was probably banging her head on the toilet. If that was the case that had to make some noise.
The police interviewed mom and said they don't believe she knew at all what was going on up there. But how awful for her.............she's going to have to live with the "what ifs?" for the rest of her life. Even if she did hear a noise, who knows if maybe her husband said "we're fine up here don't worry", etc.
A lot of people around here are speculating that maybe he is making up the "devil" defense just to make it seem like he is insane, because he never showed any signs of insanity before.