For days, authorities say, two South Pasadena High School students plotted a massacre for when classes resumed after summer.
They swapped ideas over Skype about using explosives and firearms to target three school staff members and kill as many students as they could, never realizing that their communications were being monitored by local law enforcement, according to police.
When confronted by investigators, the boys matter-of-factly said they had been willing to die as part of their plan, South Pasadena Police Chief Art Miller told reporters.
Miller provided new details Tuesday about the plot, saying police were able to foil what would otherwise have been a tragedy in the upscale community's public high school thanks in large part to a tip relayed to administrators at the school district that was forwarded to police.
"As they put it, they just wanted to kill as many people as possible," Miller said. "They had a very specific plan on how they were going to carry out their sick mission."
Prosecutors on Tuesday were reviewing whether to file criminal charges against the boys, who are 16 and 17. The teens were being held on suspicion of conspiracy and criminal threats, Miller said.
Police found no weapons or explosives at the boys' homes but did glean some "pretty frightening information" from computers and interviews with the suspects, Miller said. He declined to provide specifics about the alleged plot, how it was uncovered or the evidence that was found, saying the investigation was ongoing.
The arrests marked the third school shooting threat in Los Angeles County in the last few days.
Two Santa Clarita Valley teens were arrested over the weekend on suspicion of making separate threats of deadly school violence on social media. Los Angeles County sheriff's officials determined that those boys, ages 13 and 15, had made the threats as pranks that spiraled out of control. The 15-year-old boy is accused in juvenile court of making criminal threats. The 13 year old had not been charged as of Tuesday.
In South Pasadena, Miller said the threat of violence was real.
The students had researched weaponry, explosives and methods for disarming law enforcement officers who would respond to a school shooting, the police chief said. The boys, he said, also had discussed using a relative's weapon.
"This was at the very beginning of their plot to create a massacre," Miller said. The teens admitted "to wanting to carry out the threats."
One of the students resisted arrest, closing the door on officers, who forced their way into his home as he attempted to run away, Miller said. The other student was taken into custody without incident, he said.
Police did not name the students, citing their status as juveniles.
South Pasadena High School, which has about 1,500 students, is scheduled to resume classes for the fall Thursday. The school's principal, Janet Anderson, sent parents and employees an email late Tuesday saying that the threat was limited to the two students and that the school would see an increased police presence when students return from summer break.
"That presence is for reassurance and security and not due to any ongoing threat," she wrote.
News of the arrests prompted relief among some parents, even those who wondered aloud how real the threat had been.
"It's very alarming and very sad. The good thing is it was detected," said Graham Witherall, whose daughter attends the school. "I'm curious about whether this was a couple of kids fantasizing or if this was a real plot."
Deb McCurdy, the incoming president of the district's parent-teacher-student association, said she was shocked that a school shooting might have been planned in her community.
"We're stunned, but relieved the systems in place worked," she said.
Melanie Ciccone, who has a son at the high school, said the arrests were unsettling and raised several questions about the students.
"What motivated them to act this way?" Ciccone said. "Alienation? Fear?"
Michael Dorn, a school-safety expert and executive director of Safe Haven International, said far more incidents are prevented in schools than occur thanks to a growing vigilance nationwide by school officials and police to possible threats well before they are carried out.
"That is where we want to be. We don't want to be where the kids have five guns and explosives when they are discovered," Dorn said. "With most students there is no real threat, no initiative to kill, and it amounts to a hoax. But you have to look through hundreds of hoaxes to find the ones you should be concerned about."
Julian Lopez, a 17-year-old who is about to start his senior year at the high school, said he did not know the identities of the arrested students but was alarmed by the allegations because he has probably encountered them.
"Is it one of my friends? Someone I speak to in class?" Lopez said. "It just seems really scary."