Las Vegas Gunman Stockpiled Weapons over Decades, Planned Attack

Stephen Paddock, 64, the gunman who attacked the Route 91 Harvest music festival in a mass shooting in Las Vegas, is seen in an undated social media photo obtained by Reuters on October 3, 2017. Social media/Handout via Reuters

LAS VEGAS—The Las Vegas gunman who killed 58 people and himself in the deadliest mass shooting in modern U.S. history stockpiled weapons and ammunition over decades, and meticulously planned the attack, authorities believe.

But what led Stephen Paddock, 64, to unleash the carnage he did remains largely a mystery.