A second threat insinuating violence posted on social media prompted police to establish a presence on school grounds throughout Durham on Monday.
Police said they started investigating the threat made against Coginchaug High School and a staff employee last week.
"It's such a small town and no one really thought that would happen here, but it did so we're just dealing with it," one parent told Channel 3.
New complaints were reported about a student's Instagram posts. He was arrested and will not be allowed on school property.
Officials said he referenced the Florida school shooter and possible violence at Coginchaug. A school employee was also threatened.
However, the student told investigators that he never intended to follow through with anything and never considered the consequences of his actions.
Superintendent Kathryn Veronesi said she has been in touch with the student's family. She said they reassured her that their son does not and never did have access to firearms.
"We have a police officer who's in the building, one outside the building and we've been popping into classes, saying good morning and checking on them [Monday,]" Veronesi said.
She also encouraged all parents and students to immediately report any suspicious behavior or messages that are threatening or make students feel unsafe.
"I have to say, that this community and the teachers and leadership in this school have done an incredible job to make sure we're doing the things to make students feel as safe as possible, given the circumstances," Veronesi said.
The student has not been identified. Officials will only say that he is under the age of 18.
School officials said they are not taking the threats lightly. They said they are taking a strong stance.
They said the student was arrested and charged with second-degree breach of peace and second-degree harassment for the second case.
The student is expected to appear at Middletown Juvenile Court on March 7.
The increased police presence at the Regional School District No. 13 schools began at 7 a.m. on Monday.
It will remain at Coginchaug all week.
These threats closely follow another suspicious post made on social media.
State police say about a week and a half ago, Coginchaug reported a post made by a student. Police say no physical threat was made, but it was enough to cause alarm and disrupt the atmosphere at the school.
That student has been charged with breach of peace and will appear in court next week.
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