In the attack, 58 people died and nearly 500 people were hurt, some seriously.
Over the last nine days, much has been learned about the shooter, identified by police as 64-year-old Stephen Paddock, but a lot is unknown.
And because so many false stories have polluted the internet, there’s still some confusion over the details of the shooting.
One of the most persistent stories is that there is still a second person involved and another person was shooting from another window.
Las Vegas Metropolitan Police Department Undersheriff Kevin McMahill strongly denounced that theory when he spoke to KNPR’s State of Nevada Tuesday.
“I’m 100 percent confident there was one shooter,” he said.
McMahill said Paddock had 23 different types of semi-automatic rifles in his room at Mandalay Bay, which explains why some of the shots fired sound different than others.
He also reminded people that there are two windows out at the hotel but they’re for adjoining rooms and the second window allowed the shooter to aim for the fuel storage tanks at the airport.
“I completely see why people see it,” he said of the theory that there were two shooters, “I’ve spent time looking at all of the things that people have looked at. But I’m 100 percent confident that on the day of this shooting, when he was murdering so many innocent people and wounding so many others, that he was solely responsible for pulling the trigger on all of those weapons.”
McMahill also said that police have combed through hundreds of different images from surveillance cameras around the casino and have never found evidence of Paddock with someone else.
The undersheriff also addressed the video that has been circulating, which allegedly shows shots being fired from the fourth floor of the hotel.
“There are no additional broken windows," he pointed out. "There is no investigative element here that has uncovered any additional shooter in any additional location.”
Some people have also said that police didn't check the roof and someone was also firing from the roof, "we've combed that hotel entirely and we're confident there is only one shooter," McMahill stated.
He also explained the stories from that night that there were multiple active shooters up and down the Strip. He said what is likely to have happened is people who were injured ended up at other hotels and were reported as a 'shooting victim,' but that description was translated as a 'shooting' at that location.
He said teams of officers checked multiple active shooter reports at several Strip properties that night and found nothing.
Another question about the tragedy that has surfaced recently has been about the timeline.
Originally, police said Mandalay Bay security guard Jesus Campos arrived on the scene after the shooting started and saved lives by stopping Paddock from continuing to fire.
However, McMahill said that timeline has changed after speaking to Campos and others involved.
According to McMahill, Campos was checking the 32nd floor of the hotel on a report of a problem with an alarmed stairwell door. When he arrived, he noticed the door wouldn’t open. He called maintenance to the area to fix the door. While waiting for maintenance, he heard drilling sounds, which he found odd.
He went to the room where he heard the drilling. Because Paddock had mounted cameras outside his door, he saw Campos coming and shot him and fired several rounds down the hallway.
Paddock then turned his guns on the crowd.
McMahill said so far, they cannot say for sure what Paddock was ultimately planning, but he can be sure that Campos disrupted it.
“I’m confident that he was not able to fully execute this heinous plan and it certainly had everything to do with being disrupted not only by security and maintenance but by the rapid response of the men and women of Metro,” he said.
McMahill also said the reason the information is changing is that detectives are working with thousands of different eyewitnesses who are telling them different versions of what happened.
Also, in the immediate aftermath of the shooting, Metro’s first concern was making sure there weren’t any accomplices that might put people in further danger.
As far as the drilling sound Campos heard, McMahill said Paddock did drill out the peephole in the door of the room and he drilled another hole on the door frame next to a wall, but investigators can't say for sure what that hole was for.
Another part of the puzzle that police still have not figured out is what Paddock was trying to do when he shot at jet fuel storage tanks near McCarran International Airport.
McMahill said the shooter used the second room of the suite to fire on the tanks, and he struck them twice, but what his intention was is still unclear.
“So many people want answers, none more so than the local law enforcement but we may not have an answer to some of those questions as we continue forward,” he said.
Another answer they're trying to find is Paddock's plan after he was done shooting. Sheriff Joe Lombardo said in a news conference that items in the room indicated that the shooter expected to escape.
McMahill expanded on that idea saying that they found a gas mask and other items in the room that hinted at another element of a plan.
McMahill also said his car, which had explosive chemicals inside, shows there may have been more to his plan than opening fire on a concert venue.
“That leads me to believe he may have had the intention to escape from there and continue his rampage in another location,” he said.
But like so many other parts of this investigation, it remains a mystery because Paddock left no written trail of his intentions and no one seemed to know what he was planning.
Kevin McMahill, undersheriff, Las Vegas Metro Police