San Bernardino mass shooter Syed Farook had multiple photos of a Rialto high school on his cellphone, according to sources close to the investigation.

As a health inspector for the San Bernardino County Department of Health, Farook inspected the majority of Rialto Unified School District’s 30 food preparation facilities twice a year, according to the district.

According to sources close to the investigation, FBI investigators searched Carter High School in Rialto on Monday after multiple exterior photos of the school were discovered on a cellphone owned by Farook.

“We are cooperating with the FBI as well as local law enforcement,” Rialto Unified spokeswoman Syeda Jafri said Monday afternoon.

Farook’s signature, which is clearly legible on his letter grade ratings of Rialto Unified food service facilities, has been covered up by Post-it notes by staff at many of the locations, so as to not alarm patrons, Jafri said.

Rialto Unified is not the only school district where Farook inspected food service areas. On Thursday, the day after the shooting, bomb-sniffing dogs were brought into Arroyo Valley High School in the San Bernardino City Unified School District, and nine other SBCUSD campuses were searched by police.

“The bomb-sniffing canine unit from the San Manuel Band of Mission Indians searched the pool and kitchen areas at Arroyo Valley High School on Dec. 3 as an extra precaution,” said Linda Bardere, spokeswoman for San Bernardino City Unified. “Nothing unusual was found, and the site was deemed safe.”

Following the inspection, Bardere said the district established a list of all (district school) sites Farook inspected.

“Our district police department conducted inspections at the remaining sites on Dec. 3,” Bardere said. “Our officers did not find anything abnormal and deemed all of the sites safe.”

FBI officials close to the investigation say they have no definitive evidence campuses were specified targets of attack by Farook and his wife, Tashfeen Malik, who sympathized with the ISIS terror group.

Others, though, aren’t so sure.

“That tells me that he is doing close reconnaissance of a target area. They want to look at ingress routes, the egress routes and the centers of large population like a cafeteria,” said former Green Beret Lt. Col. Scott Mann, a counterterrorism expert who trained more than 15,000 special forces personnel during his 23 years in the Army. “It looks like a duck, quacks like a duck.”

And this fits with ISIS’ explicitly stated agenda, Mann said.

“ISIS, more so than al-Qaida, operates off a prophecy that they are going to usher in the apocalypse,” Mann said. “That’s what they want. They’re doing anything and everything they can to draw us in emotionally into that battle. … That’s why they’re going for the schools, that’s what they’re doing with the in-your-face violence.”