LAS VEGAS -- (KTLA) -- It took about 10 minutes for Stephen Paddock to carry out the deadliest mass shooting in modern US history.
From his position at a Las Vegas hotel, Paddock fired a barrage of bullets at 22,000 concertgoers below at a country music festival -- made possible through what appeared to be meticulous planning.
The shooter had checked into a hotel room overlooking the music festival, stocked a cache of weapons there and set up cameras inside his hotel suite and hallway.
The first call of shots being fired came Sunday, 10:08 p.m. and the gunfire stopped at 10:19 p.m., said Clark County Undersheriff Kevin McMahill on Tuesday. He said the shooting went off and on for nine to 11 minutes.
The massacre left 58 people dead and another 500 people wounded from gunshots to stampede injuries.
No one knows why Paddock gunned them down.
But authorities are hoping for clues as his girlfriend, Marilou Danley returned to the United States Tuesday night from the Philippines. She is being accompanied by the FBI in Los Angeles, where Las Vegas police plan to question her, a law enforcement source told CNN.
Police believe Paddock acted alone.
He had an arsenal of weapons, including bump-fire stocks found in the hotel, which is a legal device that enables a shooter to fire bullets rapidly, similar to an automatic rifle. Paddock had outfitted 12 of his firearms with the bump stocks, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives.
The shooter also had cameras set up inside and outside the suite. Police are not aware whether the devices were transmitting -- the FBI is investigating their use -- but the Clark County sheriff told reporters he thinks Paddock might have used them to watch for people approaching his room. One camera looked out the peephole on the suite's door.