A note with calculations of where to aim to maximise casualties was found in the hotel room of Las Vegas gunman Stephen Paddock.
The discovery, by police officers who stormed his room as last weekend’s massacre unfolded, was revealed in a TV interview.
Paddock, 64, killed 58 people from the 32nd floor room in the Mandalay Bay Hotel, which overlooked a crowd of more than 20,000 people attending the Route 91 Harvest Music Festival in the Nevada city.
The hand-written note was found near a window that Paddock had smashed to fire on the crowd, and included calculations about where to aim to kill as many people as possible in the crowd, about 400 metres away from the hotel.
David Newton, an officer with the Las Vegas Police Department’s K-9 Unit, told CBS show 60 Minutes: “I could see on it he had written the distance.
“The elevation he was on, the drop of what his bullet was gonna be for the crowd.”
“He had that written down and figured out so he would know where to shoot to hit his targets from there.”
By the time police arrived at the scene Paddock had killed himself, and his body was found surrounded by an arsenal of weapons and stockpiles of ammunition.
Many of those had been adapted to function as if they were fully automatic machine guns.
Officer Newton told 60 Minutes the room, which was filled with dust and flashing lights from an explosive used to blast open the door, was something “straight out of a movie”.
Investigators are yet to establish what may have compelled Paddock, who had no known links to radical groups and left no manifesto or messages, to carry out the massacre.