One of the ways that video poker players get an advantage is to play casino promotions, which essentially pay out bonuses to winners, said Richard Munchkin, author of “Gambling Wizards: Conversations With the World’s Greatest Gamblers.” A gambler like Mr. Paddock will often “lock” a machine, meaning he or she monopolizes it and makes sure no one else uses it during a gambling session.

For one casino promotion, Mr. Paddock showed up two hours early, locked two machines and played them for 14 hours straight, Mr. Munchkin said, based on information he had compiled from other gamblers who were there at the time. The promotion lasted 12 hours, he said, “but he wanted to play for two hours before anybody got those machines. He knew they were the best machines based on pay tables.”

Mr. Paddock “knew the house advantage down to a tenth of a percent,” he said.