Nancy Lanza loved guns, and often took her sons to one of the shooting ranges here in the suburbs northeast of New York City, where there is an active community of gun enthusiasts, her friends said. At a local bar, she sometimes talked about her gun collection.

It was one of her guns that was apparently used to take her life on Friday. Her killer was her son Adam Lanza, 20, who then drove to Sandy Hook Elementary School, where he killed 26 more people, 20 of them small children, before shooting himself, the authorities said.

Ms. Lanza’s fascination with guns became an important focus of attention on Saturday as investigators tried to determine what caused Mr. Lanza to carry out one of the worst massacres in the nation’s history.