SOLVED. Thriller about abandoned hotel [s]

[Emma]

I read this book about 13 years ago 2008 and I think it was around 8 years old at the time. I'm super hazy on the details because I was fairly young when i read it but it has stuck with me.

So spoiler alert

Its about someone investigating an abandoned hotel and the story was the builder/owner of it had agoraphobia and couldn't go outside. So he designed the building to have a network of tunnels inside the walls so he could spy on the ocuppants of the hotel.

More vague details; it had a pool in it that i think while this guy was investigating was covered up. And the pool turns out to be super important to a murder investigation. But i can not be sure.

[Emma]

Holy moly, I think that is it. Thank you ! I've been searching for this book for years because I never got to finish it.