Four people were shot at an elementary school in San Bernardino, California, Monday just after 10:30 a.m. Pacific time – and at least one leading anti-gun activist wasted no time before she faulted the National Rifle Association for "trying to force guns into schools across the U.S."

Three are dead – including an 8-year-old special needs student, a female teacher and an adult male shooter – and another student, 9, was injured after an apparent murder-suicide in a classroom at North Park Elementary School on H Street.

"We believe the suspect is down and there's no further threat," Burguan said on Twitter around midday Monday.

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The San Bernardino Unified School District sent an email to staff stating, "This is believed to be a case of domestic violence," according to the Los Angeles Times.

The shooter – the teacher's husband, who has been identified as 53-year-old Cedric Anderson, according to the Washington Examiner – reportedly came to campus to visit the deceased teacher, Karen Duane Smith. Authorities do not believe the students were targeted.

Smith carried a large caliber revolver, walked into the classroom without saying a word and shot his wife dead.

At a press conference held before 8-year-old Jonathan Martinez passed away from injuries, Capt. Ron Maass said: "The children we do not believe were targeted. The suspect had come to the classroom to visit. The adult female was in the classroom. ... 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."

North Park Elementary School has more than 500 Hispanic and low-income students in kindergarten through sixth grade, the Times reported. In its deadliest year since 1995, San Bernardino saw 62 murders in 2016 – a 41 percent increase from the previous year.

The school was put on lockdown, along with two others, Hillside Elementary School and Cajon High School. Helicopter footage showed students clustered near an exterior fence on campus while police with long guns canvassed the nearby parking lots. Students were evacuated to a physical education building at Cal State San Bernardino.

The shooting takes place just more than a year after a shooting spree in San Bernardino that left 14 people dead and 22 wounded. In December 2015, husband-and-wife terrorists Syed Rizwan Farook and Tashfeen Malik were shot and killed by police on the evening of the mass killings.

Hundreds of Twitter users sent their thoughts and prayers to the victims and their families Monday.

Education Secretary Betsy DeVos released the following statement: "My heart and prayers go out to the victims of this horrible act and to all students and members of the North Park Elementary School community. I want to thank the first responders, teachers and school administrators who were there to protect the students in harm's way. As a mother and grandmother, today's senseless violence is a tragedy no parent should ever have to face. I ask everyone to join me in keeping all the victims and those impacted in your prayers."

Others immediately seized on the opportunity to express their political views:

"Don't tell us not to 'politicize' this San Bernardino shooting. There is nothing more political than kids going to school and getting shot," tweeted Kaivan Shroff.

"So, I work in San Bernardino. To quote a friend, politicians need to show thoughts and prayers up their a--es, and actually DO SOMETHING," tweeted AnnM.

"Sure, 'pray for San Bernardino' would do, but how about instead of that being the only action taken, we actually regulate these guns?" tweeted Brian.

Shannon Watts, founder of the anti-gun group Moms Demand Action, wasted no time after the shooting before she condemned the National Rifle Association.

Watts tweeted: "This is the exact right time to remind every American that the @NRA is fighting to force guns into schools across the US."

Actor Wil Wheaton, who played Wesley Crusher on the TV series "Star Trek: The Next Generation," tweeted: "F--k the NRA."

Talk-radio and TV host Dana Loesch, a national spokeswoman for the NRA, blasted Watts for seizing on the tragedy to push her anti-gun views.

"Please demonstrate class and stop politicizing tragedies," Loesch tweeted. "CA has all the gun laws you wanted, so what happened?"

Others posted the following responses to Watts' tweet: