Something similar happened here in Denver.
Unknown targets hidden behind hidden walls can be a recipe for disaster.
http://www.rockymountainnews.com/new...ears-slayings/
In this case, the shooter was being a fricking dumbazz, but it can happen with any discharge of a firearm.
If you are in a house or near any penetrable objects that could hide a person from your view, best to take a shot from the knee, shooting upward at your target if at all possible. There is a lot more wood and ability to stop a bullet in the roof structure than in the walls. Also, a bullet falling from the sky is pretty much harmless given enough distance to make a more downward trajectory than horizontal.