The teen was arrested after the school's resource officer was alerted by staff members that an unauthorized person had entered the school, Yorktown Police said.
As the officer searched for the teen, the school was placed on lockdown, while additional officers responded to the scene, police said.
The teen, a former student, was quickly located, arrested and charged with criminal trespass.
He was later released to his parents on his own recognizance. He is scheduled to appear in court Oct. 26 to face the charges.
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