LAS VEGAS — The high-stakes gambler responsible for the deadliest mass shooting in modern U.S. history sought notoriety in the attack but left his specific motive a mystery, the FBI said Tuesday as it concluded the investigation of the 2017 massacre that killed 58 country music fans.

While the agency found no “single or clear motivating factor” to explain why Stephen Paddock opened fire from his suite in a high-rise casino hotel, Paddock may have been seeking to follow in his father’s criminal footsteps, the FBI said.

“It wasn’t about MGM, Mandalay Bay or a specific casino or venue,” Aaron Rouse, the agent in charge of the FBI’s Las Vegas office, told The Associated Press. “It was all about doing the maximum amount of damage and him obtaining some form of infamy.”

Paddock’s physical and mental health was declining. His wealth had diminished, and he struggled with aging, federal agents said. The findings were contained in a long-awaited report compiled by the FBI’s Behavior Analysis Unit, a group of experts who spent months examining several factors that might have led to the rampage.

“This report comes as close to understanding the why as we’re ever going to get,” Rouse said.

The 64-year-old, who acted alone, fatally shot himself as police closed in. Almost 900 people were hurt during the Oct. 1, 2017, attack on an outdoor concert.

Paddock was inspired in part by his father’s reputation as a bank robber who was once on the FBI’s most wanted list, the report said. In many ways, he was similar to other active shooters the FBI has studied — motivated by a complex merging of development issues, stress and interpersonal relationships.

His “decision to murder people while they were being entertained was consistent with his personality,” the report said.

The gunman was not directed or inspired by any group and was not seeking to further any agenda. He did not leave a manifesto or suicide note, and federal agents believe he had planned to fatally shoot himself after the attack, according to the report.

Paddock was a retired postal service worker, accountant and real estate investor who owned rental properties and homes in Reno and in a retirement community more than an hour’s drive from Las Vegas. He also held a private pilot’s license and liked to gamble tens of thousands of dollars at a time playing video poker.

His younger brother, Eric Paddock, called him the “king of micro-aggression” — narcissistic, detail-oriented and maybe bored enough with life to plan an attack that would make him famous. His ex-wife told investigators that he grew up with a single mom in a financially unstable home and he felt a need to be self-reliant.

Police characterized him as a loner with no religious or political affiliations who began stockpiling weapons about a year before the attack. He spent more than $1.5 million in the two years before the shooting and distanced himself from his girlfriend and family.

The night of the massacre, Paddock used assault-style rifles to fire more than 1,000 rounds in 11 minutes into the crowd of 22,000 music fans. Most of the rifles were fitted with rapid-fire “bump stock” devices and high-capacity magazines. Some had bipod braces and scopes. Authorities said Paddock’s guns had been legally purchased.