Police on Monday arrested two students suspected of planning a mass school shooting that targeted teachers and students at South Pasadena High School.

School officials reported the suspected plot to police on Thursday, but did not say how they learned of it. The pair had been under surveillance since the report, South Pasadena police Sgt. Brian Solinsky said.

He would not elaborate on the plans or what form they took, but Solinsky said they were “very specific” and included named targets.

“This is a prime example of school officials recognizing suspicious behavior,” Solinsky said in a statement. “It was this information that helped prevent a horrific tragedy.”

Police found no weapons in either of the student’s possession or in their homes, authorities said.

“Any time something like this comes up, it certainly causes great concern, not just for South Pasadena, but public schools across the country,” South Pasadena Unified School District Superintendent Geoff Yantz said.

Police said they did not find guns or other weapons in the boys’ homes. However, officials said the boys had been researching weapons on the internet.

A spokeswoman with the Los Angeles County District Attorney’s office said she was uncertain if charges had been presented by police.

Sgt. Robert Bartl said the suspects researched rifles, handguns, submachine guns, bombs and explosives, specifically propane.

“They were researching weapons and how to fire and assemble them,” Bartl said.

Bartl said a submachine gun can fire several rounds per second and can “cause catastrophe.”

The boys told police during the investigation what they had researched. Police did not know when they were planning to carry out the shooting.

Bartl said detectives obtained evidence where the boys listed the names of three teachers and two students who they wanted to kill.

Their identities were not available.

Los Angeles County criminalists Monday searched the suspects’ computers’ for files and history, Bartl said.

South Pasadena Police officials plan to hold a news conference Tuesday morning to discuss the arrests.

“I don’t know how it was reported to (the school), they got knowledge from some source and then it was reported to us,” he said.

Patrol officers were immediately sent to the school to take an initial crime report and detectives followed leads and tips, Bartl said.

“Detectives served warrants at each of the suspect’s homes,” officials said. “Enough evidence was discovered, and based on that evidence the suspects were arrested at their homes.”

One of the suspects was arrested without incident.

The second suspect resisted arrest and officers had to force entry into his house, officials said. Reportedly, he was captured in the home as he tried to run away from the arresting officers.

“School doesn’t start until Thursday and that was one of our goals — to make sure the investigation was moving very quick,” Bartl said. “(We) had detectives working nonstop the last four-to-five days since we received the actual report so that we could put a stop to this prior to school starting.”

“(We’re) pretty confident that we’re going to find more evidence on the computers, and through their statements to us, that they were using their computers to research weapons,” Bartl said.

Detectives have not spoken to any students, but spoke with the teachers who were named on the suspects’ list, Bartl said.

Yantz did not know how long the three teachers have been employed with the school.

“We will be providing support services to students, faculty and employees who feel the need to have such support,” Yantz said. “As a precautionary measure there will be additional police presence on campus to start the school year.”

Yantz did not comment on whether or not the school had past issues with the suspects.

A letter was sent out Monday night via email to parents notifying them of the incident and offering counseling for students.

Bartl said the boys planned to carry out their attack for personal reasons.

“They may have been crossed by one of the students or teachers, maybe by how the teacher taught or a grade (one of the suspects) received,” Bartl said. “It was definitely directed toward people they weren’t happy with.”

On May 6, 1940, a South Pasadena school principal, angry about being fired by the district, shot and killed five school officials in what is now considered a mass school shooting.

No additional suspects are being sought in connection with the recent planned shooting, Bartl said. Police said they will give an update at a news conference at 10 a.m. Tuesday.

Anyone with more information is asked to call South Pasadena Police Department Detectives at 626-403-7297.