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After being admitted onto the campus of North Park Elementary School in San Bernardino, a 53-year-old Riverside man went to his estranged wife's special education classroom and opened fire Monday, fatally shooting her and striking two students before killing himself, police said.

One of the students, an 8-year-old boy named Jonathan Martinez, died after being rushed to the hospital.

The teacher was identified as Karen Elaine Smith, 53. Her husband, the shooter, was identified as Cedric Anderson of Riverside, also 53.

Without saying anything, Anderson quickly opened fire with a large-caliber revolver, killing Smith and striking two students who were standing behind her, according to San Bernardino Police Department Chief Jarrod Burguan.

He reloaded at least once, the chief said.

Fifteen students between first and fourth grades were in the special education classroom, as were two adult aides.

Authorities responded to the elementary school, located at 5378 N. H St., to a report of an active shooter just before 10:30 a.m., according to San Bernardino City Unified School District spokeswoman Maria Garcia.

When officers arrived, they found a man and a woman dead in a classroom, as well as two injured students, Burguan said. The gunman was among those who were down, according to the chief, who said there was no further threat to the school.

The two students who received gunshot wounds were taken to Loma Linda University Medical Center's trauma center; both were initially listed in critical condition. Martinez died shortly after arriving at the hospital.

Burguan later said the surviving student was a 9-year-old boy who was in stable condition.

The motive for the shooting was not immediately known. The couple had only been married for a few months and had been separated for a month or so, Burguan said.

Anderson has a criminal history, including domestic violence, weapons and possible drug charges, according to the chief. It's not clear what charges, if any, Anderson has been convicted of.

Before the victims were identified, San Bernardino police Capt. Ron Maass said at an early afternoon news conference that the gunman had gone to the classroom to visit the adult female victim.

The children were not the gunman's targets, the captain said.

"We believe the two children were the unfortunate recipients of injuries by being in the proximity to the female at the time of the incident," Maass said.

The parents of both student victims have been notified.

"This is a tragic incident that has befallen our city," police Lt. Michael Madden said at the news conference.

Before going to the classroom, the shooter checked in at the school's front office, which is the only point of entry to the campus while classes are in session, school district Superintendent Dale Marsden said. About 500 students attend the school.

Burguan noted that it's not uncommon for a spouse to come onto campus and request to drop something off with a teacher, which is what Anderson did.

The elementary school does not have uniformed police officers or campus security, unlike the district's middle and high schools, according to Garcia.

"Our middle schools have campus security and all of our high schools have uniformed police officers,” she said.

Garcia explained that the district re-examined its security measures after the Dec. 2, 2015, terror attack that left 14 dead at the Inland Regional Center, which is about 7 miles south of North Park. All district principals have had lockdown training and know "exactly what to do" if there's an active shooter report, she said.

“Especially after Dec. 2 we actually took a closer look at all of our campuses and what we can do to increase student security and campus safety. The majority of our principals have participated in lockdown training … They know exactly what to do and what they need to do to keep students safe,” Garcia said.

The first units arrived on scene within seven minutes of getting the call, Burguan said. Within minutes, eight officers were at the school.

The San Bernardino County Fire Department first confirmed there were multiple victims at approximately 10:45 a.m., but did not provide a count.

Students at Cal State University San Bernardino, which is not far from the elementary school, were asked to shelter in place amid the active shooter report, the university tweeted. The shelter in place order was removed about an hour later.

North Park parents and guardians were asked to go to Cajon High School and have a picture ID in order to pick up their students, the school district tweeted. Some parents expressed confusion after contradictory information was released about where students could be picked up.

“If parents are looking to reunite with their children, all kids are being transported to Cajon High School,” Garcia said.

All students were evacuated from the North Park campus by noon, according to the district spokeswoman.

Some students may need to be interviewed by authorities, which could take up to three hours, authorities said. Police urged parents who were going to pick up their children to be patient.

The students are being "well cared" for at Cajon, according to police spokeswoman Lt. Vicki Cervantes. She tweeted that the children had snacks, played games and watched a Disney movie as they waited to go home.

In addition to North Park, Cajon Elementary School and Hillside Elementary School were also initially placed on lockdown, according to the school district.

North Park Elementary will be closed for at least the next two days. Parents with questions are urged to call the district office at 909-381-1100.

The county's Department of Behavior Health tweeted that it was monitoring the situation and was preparing to deploy health crisis teams to the school, as needed.

A team of 12 victim advocates are assigned to help parents and students, San Bernardino County District Attorney Mike Ramos said. Any parent who needs help should call the DA's victims' services department at 909-382-3846.

DBH has established a behavioral health crisis line in #SBCounty (909) 386-8256 or (888) 743-1478 #NorthPark #SanBernardino — San Bernardino DBH (@sbdbh) April 10, 2017

KTLA's Jennifer Thang, Anthony Kurzweil and Nisha Gutierrez-Jaime contributed to this story.

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