Two years have now passed since the deadliest mass shooting in modern U.S. history – yet the biggest question about it remains unanswered.

The American public is still in the dark as to why Las Vegas gunman Stephen Paddock opened fire on concertgoers outside the Mandalay Bay resort on Oct. 1, 2017, killing 58 and wounding hundreds more.

The FBI’s agents and behavior specialists spent more than a year investigating the attack. Officials released clips of nearly 1,200 officer body camera videos, many hours of 911 audio recordings and dozens of handwritten and transcribed witness accounts.

But 730 days later, no one can definitively say what Paddock’s motive for the massacre was.

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Paddock acted alone when he planned and carried out the attack, Aaron Rouse, the special agent in charge of the FBI’s Las Vegas office, said in January. The 64-year-old fatally shot himself as police arrived into his hotel suite.

Las Vegas police closed their investigation in August 2018 without establishing a motive.

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 hour’s drive from Las Vegas. He also held a pilot’s license and liked to gamble tens of thousands of dollars at a time.

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Police characterized him as a loner who had no religious or political affiliations, despite reports he had ranted about the Federal Emergency Management Agency “camps” set up after Hurricane Katrina and deadly standoffs between law enforcement officers and militia groups at Waco, Texas, in 1993 and Ruby Ridge, Idaho, in 1992.

Authorities said he began to stockpile weapons about a year before the attack and spent $1.5 million in the two years before Oct. 1, 2017. He also started to distance himself from his girlfriend and family.

Paddock sent his girlfriend, Marilou Danley, to visit her family in the Philippines two weeks before the attack. He also wired her $150,000 while she was there. She returned to the U.S. after the shooting and told authorities he had complained that he was sick and doctors told him he was suffering from an incurable “chemical imbalance.”

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In the days before Paddock fired more than 1,000 rounds with assault-style rifles into a country music festival, video footage showed him wheeling bag after bag into his hotel suite while security guards helped him. More than 30 video clips have been released showing Paddock interacting with Mandalay Bay staff, playing the casino’s gaming machines and transporting the bags.

Despite police finding 23 weapons in Paddock’s room after the shooting, he left no note to explain the chaotic mess he left behind.

As part of the memorial events this year, officials held a Sunrise Remembrance ceremony to honor the 58 that were killed.

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“All through the darkness came out an immense light,” Gov. Steve Sisolak said Tuesday morning. “Our Las Vegas family showed its true colors like never before. To give blood, to give comfort, to give support and to push through the next day and the next and the one after that.”

The Nevada DMV also released “Forever Strong” license plates today, with proceeds going toward the Vegas Strong Resiliency Center, described as a “place of healing and support dedicated to serving as a multi-agency resource and referral center for residents, visitors and responders affected by the shooting at the Route 91 Harvest Festival.”

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Lacey Newman was shot in the leg during the attack but managed to keep running. She's now an advocate for a company called citizenAID that offers a cellphone app, online training, and a bandage kit to help people injured in shootings or accidents.

"Our mass shooting was the beginning of change in how a lot of us see the world," Newman, who lives in Huntington Beach, Calif., told the Associated Press. "That's a powerful thing. You just never know when something bad is going to happen."

Fox News’ Ryan Gaydos and the Associated Press contributed to this report.