Vegas attack meticulously planned: cops

The Las Vegas gunman who killed 58 people and himself in the deadliest mass shooting in modern US 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.

"What we know is that Stephen Paddock is a man who spent decades acquiring weapons and ammo and living a secret life, much of which will never be fully understood," Clark County Sheriff Joseph Lombardo said at a news briefing on Wednesday night. Police recovered nearly 50 firearms from three locations they searched.

Some 489 people were also injured when Paddock strafed an outdoor concert with gunfire on Sunday night from his 32nd-floor suite of the Mandalay Bay hotel on the Las Vegas Strip. He then took his own life.

Paddock's girlfriend Marilou Danley was questioned by the FBI on Wednesday and said in a statement she was unaware of the Paddock's plans.