Published Monday, Aug. 18, 2014 | 6:55 p.m.
Updated Tuesday, Aug. 19, 2014 | 10:52 a.m.
Police say they arrested two high school students suspected of planning a massacre at a school after investigators monitored their Internet activities.
South Pasadena police Chief Arthur Miller said Tuesday that school officials had heard about the plot and informed police, who determined the threat was credible.
Miller said his officers saved lives by thwarting the attack in the Los Angeles suburb of about 25,000 people known for its high-quality schools.
Police say the boys, ages 16 and 17, didn't have weapons but were researching automatic weapons and explosives, especially propane.
The two teenage boys were arrested on charges of making threats and conspiracy. It was unclear when the attack might have occurred.
The FBI has joined the investigation.
Police have not named the boys.