Thomas Crooks’ cellphone was pictured alongside a remote transmitter and his dead body atop the manufacturing plant from where he shot at former President Donald Trump — as it was revealed that he asked his boss for a day off work because he had “something to do.”

The gray, 12-button remote and the “newer model” phone were recovered from the 20-year-old’s body on top of the AGR International Inc. complex after a Secret Service sniper team fatally shot him during Saturday’s rally, according to photos obtained by WPXI.

The transmitter is believed to have been connected to an explosive device found inside Crooks’ car as investigators suggested that he had planned to stage a distraction during the shooting.

Crooks was spotted by law enforcement with a rangefinder and looking at the phone nearly an hour before Trump took the stage, law enforcement sources told the outlet.

He first raised suspicion around 3 p.m. — nearly three hours before the shooting — when he passed through the security screening area with the rangefinder, according to CNN.

A rangefinder is a device similar to binoculars used by hunters and target shooters to measure distances for long-range shots.

Investigators’ working theory is that Crooks went to his car to retrieve the AR-style rifle he stole from his father, the outlet reported.

WPXI reported that Beaver County cops noticed a suspicious man on the roof, took a picture of him and reported it around 5:45 p.m.

Seconds before Crooks took his shot at Trump, a local cop interrupted the shooter, who pointed the AR-style rifle at him before the cop dropped and fell eight feet to the ground.

Although a bullet only grazed Trump’s right ear, Crooks killed hero firefighter and father Corey Comperatore, who was at the rally with his wife and daughters.

The 50-year-old dad shouted “Get down!” and used his body to shield his family from the gunfire before he was fatally shot, his heartbroken wife told The Post from her Sarver, Pa., home Monday.

Two other rallygoers were also injured.

Crooks, who worked at Bethel Park Skilled Nursing and Rehabilitation Center, allegedly told his colleagues he would see them Sunday.

The gunman had requested July 13 off, telling his boss he had “something to do,” sources told CNN.

Moments before the shooting, one of the four Secret Service counter-assault teams observed Crooks looking at them through the rangefinder.

“They were looking at him while he was looking at them,” an official told the outlet.

He accessed the roof by climbing on top of the building’s air condition system before hoisting himself up.

Investigators reportedly found a bulletproof vest, three fully loaded magazines, and two remote-controlled explosive devices in Crooks’ car, CNN reported.

Two sniper teams were set up on roofs near the location Crooks shot from, WPIX said Tuesday, citing multiple Pennsylvania county law enforcement sources.

No Secret Service team was set up on the roof where Crooks was because it was too slanted, embattled Secret Service Director Kimberly Cheatle said Tuesday.

Cheatle admitted the agency knew the building rooftop was a security vulnerability but opted not to position agents there, leaving it wide open for Crooks to get an unobstructed view of Trump on stage.

The phone found on Crooks’ body is one of two being investigated by the FBI, which also found a cellphone with a dead battery at his parents’ home in Bethel Park, Pa., according to the Washington Post.

Investigators had sent the phone found on the shooter’s body to the FBI office in Pittsburgh to open but it did not have the technology to do so.

The device was sent to the FBI’s laboratory in Quantico, Va., where agents used technology from digital intelligence company Cellebrite to open it in 40 minutes, the outlet reported.

The investigation into the phone, first reported by The Post, found few answers, leading investigators to turn to Crooks’ laptop.