I have always been in favor of some sort of proper storage mandate. Considering that around half of the shootings I've read about, going as far back as 1974, have been perpetrated by teenagers who can't legally purchase or own a gun, its obvious the majority stole their weapons for their rampages.
Also speaking personally, when I was very young and growing up, both my parents owned their own grocery stores and owned a firearm for each. One day, while sneaking around my parent's bedroom, like little children are prone to do, I found their revolver under the pillow of their bed. I remember being ABSOLUTELY terrified seeing it thanks to viewing countless number of after school specials where kids were accidentally killed playing with their parents'/relatives' unstored weapons. I slowly put the pillow back on top of the gun and backed out of the room.
That was EXTREMELY stupid of my parents, and anyone else who doesn't lock up weapons when they have or have the possibility of minors or the mentally ill in their home.