Another one for you Annele
Water came out of the shower head, but at such a rate that it would take hours to fill the shower. When you put the DI in the shower, he hit his mouth and one of his teeth feel out. After regaining consciousness, he held this tooth to the glass and hit it hard, so that the shower glass shattered. (If you've seen Sherlock S2 E3, its like that but with a tooth instead of a diamond). 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.