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Good morning.

Here’s what you need to know:

• Seeking a motive in the Vegas massacre.

Stephen Paddock, who the police say unleashed one of the deadliest shootings in U.S. history before killing himself, led an unconventional life. A high-stakes gambler whose last known full-time employment was 30 years ago, Mr. Paddock, 64, lived in a retirement community in Mesquite, Nev. Here’s what else we know about him.

Our full story about Sunday’s attack in Las Vegas, which left at least 59 people dead and more than 520 injured, is here.

Twenty-three firearms were found in Mr. Paddock’s suite on the 32nd floor of the Mandalay Bay Resort and Casino. Two of our reporters who are former Marines explain why it was a particularly effective vantage point to inflict carnage on the more than 20,000 people attending an outdoor concert below.