Watch: Teen arrested on suspicion of making death threats to Santa Clarita Valley students online.

A 15-year-old boy arrested Sunday on suspicion of posting death threats on social media aimed at students at schools in the Santa Clarita Valley apparently did so as a prank, authorities said.

Los Angeles County sheriff’s deputies began investigating the threats late Saturday after receiving dozens of phone calls about posts on Instagram from someone threatening to shoot high school students on an unspecified date, authorities said.

The boy, who was not named because he is a minor, is a student at a local high school and wrote the posts to get a reaction from his friends, realizing too late that they had been taken seriously, according to the Sheriff's Department.

The suspect "actually had no intention of carrying out these threats," said Deputy Joshua Dubin, a department spokesman. "We still take it very seriously."

Deputies worked with the William Hart Union High School District and Instagram to identify the suspect and arrested him after serving a search warrant at his home Sunday morning, said Dubin, speaking at news conference peppered with questions from concerned parents.

Detectives found information that shows the suspect acted alone and did not plan to carry out the threats. No firearms were found during a search of the home, and the suspect's family does not own any guns.

The boy's parents have cooperated with the investigation, Dubin said.

The posts, which have since been deleted, included racist and sexist remarks, as well as threats against women and minorities, authorities said.

“We are aiming our guns mostly at high school students … blood will be shed and families will suffer,” one post said, according to KTLA.

The posts also included photos of guns, dead bodies and a school marquee for a “Valencia High School,” all later found to be stock images found on the Internet.

“Valencia High School has been nominated to be shot up first,” another post said.

Some of the posts had responses voicing support of the plans. The photo depicting Valencia High School was not of the school in Valencia, but another school with the same name, authorities said.

District spokeswoman Gail Pinsker said the district takes the threats seriously and has a zero-tolerance for such acts.

"There will be consequences for any student who pulls a prank like this," she said.

Karin Tucker, who has four children at local schools, said her daughter, an eighth-grade student, came to her about 11 p.m. Saturday and told her she needed to show her something.

Tucker was putting her younger children to bed and asked her daughter to show her later.

"She told me 'No, I have to show you now," Tucker said. After viewing the posts, the quickly called the sheriff's officials, who were already aware of the posts.

"It's very disturbing," she said. "When someone puts that out there, it makes other crazy people think about things. We have to make sure the children are safe tomorrow."

There will be an increased law enforcement presence at all schools in the area, Dubin said.

Tucker was initially reluctant to send her children to school Monday, but was convinced by the increased security.

"They'll be in school tomorrow," she said.

Darlene Hamilton, who works as a campus supervisor at Saugus High School, said she normally feels very safe at school, but after seeing the threats online she was shaken.

"I'm the first one they see at the front gate," she said.

stephen.ceasar@latimes.com

Twitter: @stephenceasar