PLYMOUTH TOWNSHIP, Pa. -- A local teen hailed as a hero for helping to prevent a school massacre is now under arrest, charged with breaking into the house of the boy who planned the school attack.

The whole thing started in October, NBC 10's Deanna Durante reported.

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The teenager who pleaded guilty to planning a Columbine-like attack that was never carried out at Plymouth-Whitemarsh High School is serving years at a Montgomery County juvenile detention center facility.

Sources told NBC 10 the whistleblower in that case is among three teens accused of breaking into the home of Michelle Cossey and stealing video games and other items. Cossev's son is the 14-year-old who admitted to the school attack plot.

Cossey has been charged with a number of crimes. Prosecutors allege she purchased weapons for her son and allowed him to have a stockpile of BB guns, explosives, bomb-making books, violent videos and games. All of these items were confiscated after her son's arrest.

Prosecutors said the 14-year-old, who was not a Plymouth-Whitemarsh student, confided in a friend who attends the school. That friend blew the whistle, telling his parents and police of the plot.

Now, it's the tipster who is in trouble with the law.

Multiple sources confirmed to NBC 10 that the teen and two other P-W students are charged with burglary, theft and a number of other crimes after breaking into the Cossey home and stealing items from inside.

The three teens, accompanied by their parents, turned themselves in to Plymouth Township police Thursday night. NBC 10 is withholding their names because they are all charged as juveniles.

Sources said the alleged burglaries happened in January and late February, and the teens were bragging about the heists at school. A school administrator apparently heard the rumors and notified police.

The whistleblower had been hailed as hero, given accolades and awards multiple times for his role in alerting police to the planned attacks.

On Friday morning, that teen and his two friends will appear before a juvenile judge, Durante reported.