When the anniversaries of the Oklahoma City bombing and the shootings at Columbine High School roll around each year, emergency officials go on high alert.

So when Seneca Valley Intermediate School officials turned up two handwritten bomb threats on the first of the consecutive dates, April 19, administrators switched into what Jackson police call "lockdown mode."

Three girls, ages 14, 14 and 15, were later arrested and taken into custody in connection with the threats, police said. The suspects face four charges, including threatening to use weapons of mass destruction. The girls come from Cranberry and Jackson, although officials would not specify which girl lived where.

The school spokesperson, Linda Andreassi, would not say whether the girls were expelled. "Our discipline policy states that in similar situations, suspension should be immediate and expulsion would be recommended."

The first note was picked up at about 11:30 a.m. outside the main office and brought to the attention of school officials. It stated the school would be blown up before seventh period, according to Jackson Police Chief Len Keller. When somebody turned up a similar note in the girls' restroom, the school called in the threat. Police, fire, medical teams came, and four canine units swept through the halls.

The last bomb threat at the middle school was roughly two years ago, Andreassi said.

Seneca Valley was not the only hot spot on April 19.

"If you look around Western Pennsylvania, there were a number of bomb threats in the school districts on that day," said Keller.