Two adults and one student were killed and another student was left wounded following an apparent murder-suicide that occurred at North Park Elementary School in San Bernardino Monday morning.

The shooter, 53-year-old Cedric Anderson entered a special ed class for students with intellectual disabilities, taught by his wife, Karen Elaine Smith. He pulled out a concealed .357 revolver and opened fire on Smith, killing her and injuring two students that were standing behind her.

The student victims are an unidentified 9-year-old and 8-year-old Jonathan Martinez. Martinez sustained critical wounds and was airlifted to Loma Linda Medical Center, where he was later pronounced dead. His classmate is currently hospitalized and is in stable condition.

Police responded to reports of gunfire on the school campus and found two deceased adults, later identified as Anderson and Smith, and the two injured students.

The school and surrounding schools were placed on lockdown during the investigation, and students of North Park Elementary School were temporarily transferred to Cajon High School for their safety. Students were later transferred to the Physical Education building of the Cal State San Bernardino campus, where they were able to drink water, use the restroom and play with toys provided by the college.

“We believe this to be a murder suicide. Happened in a classroom. Two students have been transported to the hospital,” Police Chief Jarrod Burguan updated on his Twitter.

San Bernardino’s Police Capt. Ron Maass said Anderson was able to check in with school officials, despite having a gun on his person. San Bernardino Unified School District spokeswoman Maria Garcia confirms that despite “very, very tight” security, Anderson managed to “follow the check-in protocol,” by using a photo ID and signing in at the front office, and entered with the handgun.

Anderson was reportedly estranged to Smith, and the incident stemmed from an alleged domestic dispute between the couple.

“This is believed to be a case of domestic violence,” read in email submitted to North Park. Despite the lockdowns of local schools, the incident is believed to be isolated to the North Park campus.

“The children, we do not believe were targeted,” Maass said. It is unclear how many rounds were fired.

Maria Ramos, whose grandson is enrolled in North Park, reported tried to pick up the child after hearing about the shooting, noting that he was shaken by the incident.

“It was a typical morning and then chaos broke out,” Ramos told news station KABC-TV. “[He] was crying. He’s scared.”

“We want to minimize the trauma that not just our students, but our staff, have been exposed to,” Garcia said.

In 2016, 62 shooting were reported in the City of San Bernardino, a 41 percent increase from the year prior.

This incident takes place less than two years following the 2015 San Bernardino attack, a terrorist attack by a US born Pakistani couple inspired by foreign terrorist groups that killed 14 people and injured 22, and brought concerns of gun control and regulations further into the public consciousness.

The schools are confirmed to remain closed Tuesday and Wednesday of this week, but classes may continue afterward in an alternate location if the school is still an active crime scene.