Las Vegas gunman Stephen Paddock coolly calculated the geometry of mass murder, according to new details of the note he left behind on the nightstand of his hotel suite.

The slip of paper contains the handwritten calculations of his elevation and distance from the 20,000 concert-goers below — and shows he spent time mathematically maximizing his firing accuracy so he could kill as many people as possible.

“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,” Officer Dave Newton of the Las Vegas Police Department tells “60 Minutes” in an interview set to air on Sunday.

“So he had that written down and figured out so he would know where to shoot to hit his targets from there.”

The CBS news program will feature interviews with Newton and two other police officers — the three cops who used an explosive blast to break down Paddock’s door on the 32nd floor of the Mandalay Bay Casino and Hotel last Sunday night.

“Very eerie,” Newton tells correspondent Bill Whitaker of Paddock’s hotel room.

Smoke from the blast had set off a blinking fire alarm in the room. “Yeah, the dust from the explosive breach,” said Newton, a cop with the K-9 unit.

“And then you have the flashing lights,” Newton said.

“And that looked straight, like, out of a movie, you know?”

It was Newton who describes the note on a nightstand near one of the two windows Paddock broke before aiming for the crowd 400 yards away, killing 58 people and injuring hundreds more in the deadliest mass shooting in modern American history.

In Vegas on Saturday, Vice President Mike Pence and wife Karen told a crowd at City Hall that America will always remember the “courage” of the victims. “We do not grieve like those who have no hope,” Pence said. “Because heroes give us hope.”

The veep’s remarks came as FBI agents carefully hauled away the piles of backpacks, purses, baby strollers and lawn chairs left behind by concert-goers as Paddock’s bullets flew.

The belongings will be catalogued and returned to families, officials said.

Also Saturday, the family of shooting victim John Phippen, 56, asked a judge to appoint an administrator to Paddock’s estate — a first step toward a lawsuit.