Two teenagers are under arrest for allegedly plotting what the FBI is calling "a mass casualty attack" at a Houston-area high school.CBS Houston affiliate KHOU-TV reports that Spring Branch Independent School District police say evidence suggests the suspects,

The two girls, ages 15 and 16, planned on placing pipe bombs around the school and using guns to then pick off panicking students and teachers, the Montgomery County Sheriff’s Office alleged.

Evidence suggests their intent was to carry out acts of violence at a school in the Spring Branch Independent School District, law enforcement said.