So there is a reason to violate a person's constitutional rights since they owned a firearm, apparently fully in compliance with another constitutional right?
It's legal to own a firearm with certain restrictions (it must be registered, for one).
It's legal to discharge a firearm with certain restrictions (in areas designated for hunting or in shooting ranges, for example).
Just because a person can legally own a gun doesn't mean they can legally fire it anywhere they please. I'm sure a lot of cities have ordinances against firing a weapon in a residential district. And if someone is injured by gunfire (as in this case), I think a police investigation, including a search of the premises, is pretty easy to justify.