When retiree Stephen Paddock checked into his 32nd-floor hotel suite at the Mandalay Bay Resort and Casino last Thursday, nothing appeared unusual.
Housekeepers said they "saw no signs of anything" suspicious, Nevada Rep. Dina Titus told CNN.
Paddock had a "pretty well hidden" arsenal, she said.
Authorities believe Paddock brought the weapons into the hotel by himself but did not provide specifics.
By Sunday, as the Route 91 Harvest Festival, taking place in an open-air, ground level venue just hundreds of yards away from his suite, was drawing to a close, Paddock had smashed two windows inside -- one in the front and one on the corner -- and proceeded to fire, ultimately killing 59 people and injuring hundreds of others.
The attack was the deadliest mass shooting in modern US history.
Paddock had booked what Clark Country Sheriff Joseph Lombardo described as "one large suite with two rooms." The suite had uninterrupted views of the Las Vegas strip.
Paddock's victims -- concertgoers who had gathered at the music festival -- were listening to the headliner, country music singer Jason Aldean.
As the first shots rang out, first responders soon realized that the gunfire was raining down on the crowd from a higher-up vantage point. "It's coming out a window," a first responder shouts on audio obtained by CNN.
Attention soon focused on the Mandalay Bay hotel several hundred feet away. Police entered the hotel and worked their way to the shooter's sniper nest.
High up on the hotel's residential floors, a first responder radioed in: "I'm inside the Mandalay Bay on the 31st floor, I can hear automatic fire coming from one floor ahead... one floor above us."
As officers approached Paddock's suite, he opened fire, shooting a security guard in the leg, Clark County Sheriff Joe Lombardo told reporters Monday.
The first responders retreated and waited for SWAT to take the shooter out.
Clark County Assistant Sheriff Todd Fasulo said authorities recovered 23 guns from the suite and another 19 firearms from Paddock's home in Mesquite, Nevada.
Police channels identified the suite as 32135. Paddock would've had a clear view of the parking lot where the concert was being held, across the strip, around 400 yards away.
He had brought "in excess of 10" suitcases to the suite over several days, Lombardo said.
CNN law enforcement analyst Art Roddick said he was struck by the planning that went into the attack.
"Firing from an elevated position is always what you want to do so I would not be surprised if we have some video of him actually standing in that venue looking up at Mandalay Bay and trying to figure out which room is going to give him the best advantage.
"You can see those windows are knocked out, one in the front and one in the corner, which gave him two different angles to shoot from and that's all part of this planning."
The presence of other civilians staying in the hotel meant that police couldn't return fire from the ground, Roddick said.
"It's a large hotel and that's probably why it took them an hour and 12 minutes before they were able to figure out exactly which room he was shooting from and then to get to that location and figure out how they're going to do the entry."
"A team of six officers that approached security, they went up the elevators after discussing the situation with the security and obtaining intelligence," Lombardo said.
"And they checked each floor by floor until they located where they believe to be the room. Subsequently they approached the room, received gunfire, they backed off and SWAT responded."
Las Vegas Metropolitan Police Department Undersheriff Kevin McMahill said once the first responders had "isolated this individual to the two rooms, our SWAT team used the explosive breaching to go in and confront the individual."
A SWAT officer is heard on police radio: "We need to pop this (door) and see if we get any type of response from this guy. See if he's in here or if he's actually moved somewhere else."
Inside the police found the shooter dead, apparently from a self-inflicted gunshot wound. Lombardo said the police believe Paddock had "killed himself prior to our entry."
It was a threat the police could not have prepared for, McMahill said.
"These folks were attacked by a man from 32 stories up with automatic rifle fire and so I don't really know how you plan for that. We just didn't see it coming."