But he also had developed a knack for robbing banks. Over an 18-month span in 1959 and 1960, Mr. Paddock hit two branches of the Valley National Bank in Phoenix — one of them twice — and made off with $25,000, according to The Arizona Republic, citing an indictment. Each time, the report said, he showed the teller a snub-nosed revolver tucked in his belt, and fled in a stolen car that he abandoned a few blocks away to switch to the family’s new Pontiac station wagon.

When the F.B.I. finally caught up with him at a gas station in downtown Las Vegas, he tried to flee, nearly ramming an agent, before an agent fired a bullet through his windshield. He surrendered unharmed.

Mr. Paddock was convicted in 1961 and sentenced to 20 years in prison. But he escaped from the La Tuna federal penitentiary in Texas on New Year’s Eve 1968, and made his way to San Francisco, where he robbed another bank. In 1969, the F.B.I. placed him on its Most Wanted list, describing him as 6 feet 4 inches, 245 pounds and “diagnosed as psychopathic.”

“He reportedly has suicidal tendencies and should be considered armed and very dangerous,” the poster read, adding that he was an “avid bridge player.”

The youngest son, Eric Paddock, told reporters outside his Florida house on Monday that their father was largely absent from their lives. When the father died in 1998, a paid newspaper obituary listed only one son, Patrick, as a survivor.

After the 1960 arrest, the family moved to Sun City, Calif., where their mother supported the four boys, augmenting her wages as a postal worker by investing in stocks, Mr. Magee said. They never talked about their father.

Patrick Paddock II said that he and his brothers all grew up with anger that they had to learn how to manage, in his case through military training over 17 years of service in the Air Force. But he said he thought Stephen seemed the least affected. “My brother was the most boring one in the family,” Patrick said of Stephen. “He was the least violent one.”