GARLAND, Texas (CBSDFW.COM) – Two 15-year-olds and a 17-year-old have been arrested for making threats against high schools in Garland, police say.

According to police, they were informed on Tuesday of a threat made by a 15-year-old student against North Garland High School on Instagram. During the investigation, police learned of another similar threat made by another 15-year-old student against Naaman Forest High School on Snapchat.

Police say they also learned of a threat made against Naaman Forest by 17-year-old Timothy Young on Snapchat.

Police arrested Young and the 15-year-old student at North Garland on Wednesday and the 15-year-old at Naaman Forest Thursday morning.

The two 15-year-olds have not been identified due to being juveniles. All three were charged for making a terroristic threat, a third-degree felony.

“The message here is threats of shooting up a school or any threat for that matter against a school is not a joking matter and we be taken seriously and investigated,” said Lt. Pedro Barineau of Garland PD.