Someone ratted him out at school:
http://wbztv.com/local/saugus.high.school.2.606045.html
Saugus High School Locked Down For Gun Search
SAUGUS (WBZ) ― Police put Saugus High School under lockdown Friday while officers searched the school for a gun.
Someone called the superintendent's office at 10:45 a.m. claiming there was a gun in the school.
Police were called and are now in the process of going from classroom-to-classroom evacuating students as a precaution.
No one has been hurt.
11th and 12th graders are being taken by bus to a nearby American Legion Hall.
9th and 10th graders are being moved to the Blessed Sacrament Church.
Parents can pick up their children at those two locations.
Once the school is cleared, officers will sweep the building in the final phase of their search for the reported weapon.