11-year-old fatally shoots one of two intruders who broke into home, saves his 4-year-old sister

A 16-year-old who broke into the home on his third attempt was shot and killed by an 11-year-old inside the home.  Fox News has this:

An 11-year-old Missouri boy shot and killed a 16-year-old boy during an attempted home invasion Thursday afternoon, St. Louis County police said.
Police said two suspects tried to break into the home north of downtown St. Louis twice before the shooting on Thursday. On the third try, authorities said the unidentified teen went through the home's unlocked front door while the 11-year-old and a 4-year-old girl were home alone. Police said the younger boy shot the teen in the head. The would-be burglar's body was found in the home's front foyer. . . .
The second suspect fled the scene after the shooting, but was later taken into custody. . . .
Fox2Now reported that police want to know why the children were home alone and why the 11-year-old had access to a gun. . . .

While the police wanted to know why the child had access to guns, what would have happened if the 11-year-old couldn't defend his sister?  John Lott and John Whitley has this research article from the Journal of Law and Economics on the risk of requiring that guns be locked up and not accessible.

Fox News from St. Louis has this story.  The AP story on the event is available here.