Authorities identified the suspect as Glenn Litton, 56, who had a lengthy criminal record and a history of mental illness.

The suspected gunman who opened fire at a private religious school in Northern California, critically injuring two kindergarten students and later killing himself, had suffered from mental illness and made up a fake story to access the school, authorities said on Thursday.

The attack occurred Wednesday at the Feather River School of Seventh-Day Adventists in Oroville, California, while students were finishing their noon break, according to Butte County Sheriff Kory Honea. Two kindergarten boys, ages 5 and 6, sustained gunshot wounds in the shooting and remained in critical but stable condition on Thursday, Honea said.

The 6-year-old suffered two gunshot wounds that caused internal injuries and the 5-year-old was shot once in the abdomen, according to Honea. The two boys were immediately transported to trauma centers following the shooting, where they will likely undergo additional surgeries.

"They have a very long road ahead of them in terms of recovery," Honea said during a news conference Thursday. "The fact that they are currently still with us is a miracle."

Honea identified the suspect as Glenn Litton, 56, who authorities said had a lengthy criminal record and a history of mental illness. Honea said Litton may have targeted the school for its affiliation with the Seventh Day Adventist Church.

The Feather River School of Seventh-Day Adventists is a private K-8 religious school that has been open since 1965, according to its website. Honea said about 35 students attend the school.

Oroville is a town in Butte County with a population of over 19,000 people. It is about 72 miles north of Sacramento, California.

Wednesday's incident is the latest among dozens of school shootings that have occurred across the country in recent years. Several have made national headlines, sparking public outrage and debates about gun control, including the Apalachee High School shooting that left four people dead and nine injured earlier this year.

As of Wednesday, there have been at least 37 school shootings this year that resulted in injuries or deaths, according to data compiled by Education Week, a news organization that covers K-12 education.

Back-to-school reality: Campus shootings rose dramatically last year

Sheriff: Suspect used a 'ruse' to gain entry to the school

The shooting occurred shortly after 1 p.m. local time on Wednesday, according to Honea. The suspect had been dropped off at the school by an Uber driver and met with an administrator for a campus tour.

Honea said the suspect had used a "ruse" to set up the appointment with the administrator and gained campus access. Litton, using an alias, had made up a fake story about wanting to enroll his grandson at the school, according to Honea.

Following the tour, Honea said the suspect appeared to leave the school when he started walking towards the parking lot. Surveillance images then showed the suspect turning around to the playground before opening fire at students who were outside for their noon break.

"The school principal reported that she heard a loud noise, which we believe to be gunshots, and then the children screaming," Honea said. "She immediately came out, found the kids, and began rendering aid."

Several law enforcement agencies responded to the scene and discovered Litton deceased with what appeared to be a self-inflicted gunshot wound, according to Honea. A handgun was also found nearby.

Responding officers secured the campus and all students were gathered and moved to the school's gymnasium, Honea said. A school bus was later dispatched to the school and students were transported to the Oroville Church of the Nazarene to be reunified with their families.

Suspect believed may have targeted school for religious affiliation

According to Honea, Litton's criminal history — which dates to the 1990s and early 2000s — consisted of various crimes, including theft, identity theft, forgery, and fraud. Authorities said they did not find any violent crimes on his record.

Honea said authorities received information on Wednesday that led them to believe that Litton targeted the school because of its affiliation with the Seventh Day Adventist Church. The sheriff said Litton wrote a statement about carrying "countermeasures" against the school in response to the U.S.'s involvement in the Middle East.

"That's a motivation that was in his mind," Honea said. "How it was that he conflated what's going on in Palestine and Yemen with the Seventh Day Adventist Church, I can't speculate. I'm not sure that we'll ever know that."

Honea reiterated that authorities believe the attack was an isolated incident and noted Litton had "significant mental health issues." Litton's history of mental illness had been documented since he was 16 years old, according to Butte County District Attorney Michael Ramsey. Honea said authorities did not have an actual diagnosis.

According to Honea, the investigation also revealed that Litton had attended a Seventh-Day Adventist school in Paradise, a town about 20 miles northeast of Oroville, when he was younger. The sheriff added that Litton may have had a relative who attended the Feather River School of Seventh-Day Adventists as a child.

In the early 2000s, Ramsey said Litton had searched online for guns and explosives. Additionally, Litton wrote notes to himself about planning a non-specific mass incident, which Ramsey noted were "just ruminations."

Honea said Litton also had an alternative target for the attack and researched another Seventh-Day Adventist school in Red Bluff, California. Litton had scheduled an appointment with the Red Bluff for Thursday.