NASHUA — Schools in New Hampshire's second-largest district will reopen Tuesday, after law enforcement officials investigating an e-mail that vowed to harm students found "no threats" and "no devices."
The e-mail idled more than 11,000 students for one day, set off a massive law enforcement response that included the FBI and a federal bomb squad, and spread alarm among parents. On Tuesday, police will step up their presence at bus stops and other facilities, they said, to reassure residents of their safety.
The incident marked the latest in a wave of school terrorism scares that have been felt in such cities as New York, Los Angeles, and Cambridge, Mass.
Nashua Police Chief Andrew Lavoie said at an afternoon news conference that the threat targeting the city's two high schools was deemed not credible. Lavoie stopped short of calling the incident a hoax, but stressed that if caught, "the individual would be prosecuted to the fullest extent of the law."
He defended the decision to close schools, saying, "We wanted to err on the side of caution."
Superintendent Mark Conrad, who oversees Nashua's 17 public schools, said officials were alarmed by the specificity of the threat. The e-mail named both Nashua High School North and Nashua High School South as targets, specified the attack date as Monday, Dec. 21, and said how the violence would occur.
"This is not something that routinely happens in this district," he said. "We had to take it seriously."
Conrad said district officials felt that if they kept elementary and middle schools open, many anxious parents would keep their children home.
When school resumes Tuesday, Conrad said, principals will give excused absences for students whose parents are still worried and want to keep them home. Teachers will also be given talking points on how to discuss the incident with students.
"This was the right decision to take the safety of all our students into account," he said.
In an earlier statement, New Hampshire Governor Maggie Hassan backed the decision and called public safety "any government's most important responsibility — especially at our schools."
Throughout Nashua on Monday afternoon, parents, students, and residents expressed shock that a terrorism scare had come to the city.
Dave Melanson, whose two daughters attend elementary school in Nashua, said he appreciates the cautious approach of the school district.
"I'd rather be safe than sorry," Melanson said as he shopped for household items.
Tiffany Lee also said she was glad the schools were closed.
Lee has two sons in the Nashua School District, including one in high school. Lee was shopping with her son Cameron, 13, in the Nashua Mall to pass the time.
"I'm glad he didn't have to go to school today," Lee said of Cameron, although the mother worried that more threats would now be inevitable. If schools continue to close, Lee said, it only encourages "copycat" threats.
"I think it's ridiculous all the media attention we give these people," she said.
Cameron Lee said the closure gave him a momentary reprieve from a math test. Instead of cramming about inequalities, slope, and geometry, he studied a rack of new sweaters with his mother.
"I really don't know what to think," Lee said of the threat of violence. "I hope we don't have to make this up in the summer."
Michelle Espinal, a 10th-grader at Nashua High School North, said many of her classmates were excited by the news of the closures. Jennifer Espinal, Michelle's sister who graduated from the same high school, also said she was concerned when she heard about the threat.
The sisters said the school could be unknowingly encouraging violent behavior by closing because of threats, but both were glad officials took the safe course.
"It was surprising, and I was concerned," Michelle Espinal said. She was supposed to take a civics test Monday.
Instead, the unprompted day off meant Espinal could join her older sister on a trip to the mall, where the two perused the makeup aisles.
Astead W. Herndon can be reached at astead.herndon@globe.com. Follow him on Twitter @AsteadWH.