Sanford police have arrested and charged a 17-year-old boy with criminal terrorizing after he allegedly threatened on Facebook to shoot his classmates at Sanford High School.

Police were notified about the posts by the mother of a classmate at 9 p.m. Thursday. The posts had been brought to the mother’s attention by her daughter, who is a student at the school and one of those who had been threatened by name on his post.

Sanford Police Chief Thomas P. Connolly Jr. said the girl and her mother’s “swift action was crucial” in helping police address the threat.

The boy had sent individual messages to classmates that talked about shooting fellow students, and he posted a threat on his Facebook wall, a part of the social networking site that is more widely accessible to other readers.

“On that wall, he had posted his thoughts of shooting everyone in his class (Friday) and he named three specific people,” Connolly said.

Police interviewed the boy and his legal guardian late Thursday night and determined that the threat was credible – that there were “means, motive and opportunity to carry out the crime,” Connolly said.

Police searched the boy’s room and found no weapons, although there were guns in the house. They were properly secured, but if the boy was determined, he could have gained access to them, Connolly said. It’s not clear what type of guns or how many were in the house.

Connolly said the 11th-grader was cooperative. The chief would not describe the interview with the boy, but noted “there may have been some bullying issues” at school. The department’s school resource officer knew the boy, but the youth has been involved in only minor issues at school, Connolly said.

Criminal terrorizing in the adult system is a misdemeanor punishable by up to a year in jail and a $2,000 fine. Police did not identify the boy because he is a juvenile, nor did they identify the victims of the threat.

Instead of being taken to Long Creek Youth Development Center in South Portland, the boy was taken late Thursday night to a local hospital, where he was being held in protective custody Friday pending a psychiatric evaluation, police said.

Police notified the school superintendent and it was decided that because the boy was in custody, school could continue in session Friday. Several officers were posted at the campus when students arrived, police said.

“The most important aspect of this case is that a student reported her concerns about the suspect’s Facebook posts to her mother, and the mother immediately called the police and alerted us to the threat, ultimately leading to the suspect’s arrest,” Connolly said in a news release. “Since we believe that the suspect had the motive and the means to commit this crime, the student’s and parent’s swift action was crucial in allowing us to close this case.”

Later on Friday, Connolly said that news media reports about recent school shootings around the country did not influence the police response in this case, but officers were aware of them.

“We don’t have any specific information or intelligence we had anything going on here, but when you look around and see the proliferation of these events in the last couple months, it obviously concerns you,” Connolly said.

On Tuesday, a 15-year-old gunman, a student at a school near Portland, Oregon, killed another student and wounded a teacher before killing himself. In that case, police said the assault rifle and handgun the student carried had been secured but he “defeated the security measures.”

Sanford School Superintendent David Theoharides said the school takes such threats seriously and encourages students, when they become aware of a threat, to contact an adult. Theoharides said the school holds as many lockdown drills as it does fire drills.

Theoharides, who was out of state when the incident occurred, was told by administrators that there was no threat against the whole school, but just to three individuals. He was unaware of any bullying connected to the incident.

“Certainly, like all schools, we take bullying very seriously,” he said, adding that students are encouraged not to be passive witnesses to bullying. “The Internet creates a whole new venue for bullying. That’s something that’s challenging for us now.”

Theoharides said Thursday’s threats and arrest show that no community is immune.

“It reminds you all the time we’re just as vulnerable as anybody is, whether it be Newtown or out in Oregon or anywhere,” he said. “This was handled well. Unfortunately, a lot of times it is the incident you haven’t heard about.”