The portrait of Stephen Paddock that investigators have assembled stands in stark contrast: Reserved, even boring, he was an accountant and investor who liked to gamble only after calculating all the risks. Before the shooting, the authorities say, he had never broken the law. Among the many questions that are unanswered is what influence, if any, his father’s absence and infamy had on his life.

“We are establishing the timeline of the suspect’s life, his motivation and everybody else associated with him throughout time,” Sheriff Joseph Lombardo of the Las Vegas Metropolitan Police Department said. The F.B.I. has hundreds of agents on the case and more than 1,000 pieces of evidence, said Aaron Rouse, the special agent in charge in Las Vegas.

A statement from the Clark County coroner’s office said that an autopsy on Mr. Paddock had been completed, and that “multiple forensic analyses” would be performed, including an examination of brain tissue.

Benjamin Paddock had boasted during his psychological evaluation that his run-ins with authority started early and rarely stopped. He was an only child, pampered by his mother and not disciplined by his father. “I got away with an awful lot,” he told his evaluator. “I went where I felt like it, disrupting everybody’s schedule.” By 12 he was driving his own car.

He quit high school almost as soon as he started, then joined the Navy at age 15, but was discharged a few months later, he said, when the Navy figured out, “I wasn’t going to do what they wanted me to.”

He drove buses in Los Angeles, but got fired for a game of bus tag with other drivers.

In 1946 he was caught stealing a car in Chicago and reselling it in “a fraudulent fashion.” He spent five years in prison, 70 percent of it, he said, “in the hole,” or solitary confinement, because he was “unable or unwilling to abide by rules.”