The Las Vegas gunman who carried out America's deadly shooting set up cameras inside and outside the hotel room he opened fire from.
Police said Stephen Paddock put a camera in a room service trolley outside his room at the Mandalay Bay Hotel.
Sheriff Joe Lombardo said he believed this was to alert Paddock to when police were coming.
He did not give any further details or say if Paddock filmed the carnage he carried out.
Authorities were called at 10.08pm on Sunday night and Paddock fired at crowds below for around 10 minutes after that before later turning the gun on himself.
Fifty-eight people were killed and 527 injured. Of those, 50 remain in a critical condition in hospital.
In a press conference, police said they had now completed investigations at Paddock's properties.
They found five further handguns, two shotguns and a plethora of ammunition at a property in Reno.
This brings to the total amount of guns in his possession to 47.
Police also confirmed that 12 of the weapons had been modified with "bump stock" devices enabling them to discharge bullets more quickly and imitate automatic gunfire.
The authorities continued that by 10.19pm, Paddock had stopped killing, but the reason for this remains unclear, since police did not enter his room for another hour.
Police added the delay in entering the room was because Paddock had stopped firing and so they treated it as a barricade situation.
Also during the news conference they released body cam footage from Las Vegas police officers which shows them trying to locate the source of the gunfire and evacuate people from the area as shots ring out.
Detectives are still waiting to speak to Paddock's girlfriend Marilou Danley and have classified her as a "person of interest".
She arrived back in the US late on Tuesday night and was met by federal agents at the airport.
Paddock is alleged to have wired $100,000 to the country a week before the mass shooting, NBC News reported.
Paddock's still-stunned brother Eric Paddock said he suspects the money was to take care of Danley.
It is not known if the money was for her or another purpose, but authorities are hoping she will be able to answer some of the many questions surrounding the case.
The motive for the attack on people at the Route 91 country music festival opposite Paddock's hotel remains unclear at this stage.
But police said it was clearly pre-meditated from the cameras and amount of weaponry he had.
They are still investigating whether or not he was radicalised before the attack.
US President Donald Trump is due to visit Las Vegas on Wednesday.
He branded Paddock "sick and demented" a day after condemning the attack as "pure evil".
Asked if he will now consider changing gun laws, he said it will be talked about "as time goes by".