Here's another theory for you to ponder.
Water came out of the shower head, but at such a rate that it would take hours to fill the shower. Whilst you were gone, a small scale earthquake occurred and destroyed up to 3 pillars in the target stack caused a part of the ceiling inside the shower to fall and break the glass from the inside. The DI regained consciousness and then decided to repair the ceiling because he's a tad weird and likes DIY. The woman was another thief who tried to steal the ring before the DI found and poisoned her with something from the bathroom (bleach or something). After realizing his crime, the DI then moved the body into the other room, stole the ring and ran away to start a new life in Cuba.