Two teens accused of conspiring to attempt a mass shooting at their school in South Pasadena, California, were arrested Monday.

Police said the teens were planning to kill three staff members and several students at the South Pasadena High School with firearms. The authorities said school administrators tipped them off about the plot. The officials then tracked the behavior of the boys and arrested them after they collected enough evidence about their mass-shooting plans.

Officials did not reveal the identities of the teens.

"Enough evidence was discovered, and based on that evidence the two students were arrested," the South Pasadena Police Department said in a statement. "One of the students was arrested without incident. The second student resisted arrest and officers had to force entry into his residence. He was captured in the home as he tried to run away from the arresting officers."

The investigators said no weapons were found. However, the teens were planning to acquire some to execute their plot. "They were researching weapons and how to fire and assemble them," police Sgt. Robert Bartl told Whittier Daily News.

"This is a prime example of school officials recognizing suspicious behavior," police Sergeant Brian Solinsky said adding the tip off at the right time averted the tragedy, Reuters reports.

The 'hitlist' of the teens had specific targets. "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."

South Pasadena Board of Education Superintendent Geoff Yantz said Monday that the situation was under control. "Psychologists and counselors will be available at the high school to provide support to our students and employees. The School Board and I appreciate the immediate response by the South Pasadena Police Department, and school will begin on as planned," he said, reports CBS Local.

The school will re-open Thursday following the incident.

In another incident, a 15-year-old boy from Southern California was arrested for posting online threats of mass shooting in the Santa Clarita Valley area. He threatened the residents that "huge" killings will take place and "no mercy" will be shown. Police said they did not find any weapons.