CHICKAMAUGA, Ga. — Deanne Westbrook had tried everything to keep her husband, Ronald, in the house.

He was 72. Alzheimer’s had erased much of his talent for music and flying airplanes.

No one is sure how, in the frigid hours before dawn last Wednesday in this small north Georgia community near the Tennessee border, Mr. Westbrook ended up nearly three miles from home with a handful of other people’s mail, jiggling Joe Hendrix’s doorknob.

Mr. Hendrix, 34, stepped onto his porch with a Glock pistol in his hand and his fiancée inside on the phone with a 911 dispatcher. He fired four shots. One hit Mr. Westbrook in the chest.

On a cold and damp day Tuesday, Mrs. Westbrook buried her husband of 51 years, his death adding another chapter to the debate over the nation’s patchwork of self-defense laws.