Two teenage girls arrested Wednesday are accused of plotting "a mass casualty attack" at Memorial High School in Spring Branch ISD, according to authorities. The Spring Branch ISD police department was initially notified by the FBI of a potentially credible threat against the school on Tuesday and arrested the student involved,

The FBI says the plot involved pipe bombs and guns. The case spans two counties, with the girls attending two different Houston-area school districts.

Two high school students in the Houston area are in police custody and accused of plotting a “mass casualty attack” at a Spring Branch ISD campus, according to the FBI’s Houston office.