Nansemond River High School on Tuesday was the scene of Suffolk’s second known school lockdown since Connecticut’s Sandy Hook Elementary tragedy.

According to details released by the school district and city, a student used text messaging to threaten that a bomb was on a bus.

The bus and the school were searched, and a Code Red was called at the school, putting it into lockdown for an unknown length of time.

There have been no arrests in the case, which the Suffolk Fire Marshal’s office is investigating.

The first lockdown occurred the day of the shooting, Dec. 14, after a suspicious man was spotted on the grounds of Mack Benn Jr. Elementary School, which re-opened a short time later after police had spoken to the man.

The school district has admitted to a “heightened sense of security” after the Connecticut shooting.

As with school divisions across the country, Suffolk Public Schools has increased security and reviewed and tweaked policies in the wake of the shooting.

Early on Monday, senior administrators discussed the security response during a 30-minute conference at the Main Street administration offices, according to district spokeswoman Bethanne Bradshaw.

It was decided to ask Suffolk Police Department for more patrols inside and outside school buildings, particularly at elementary schools. School resource officers in middle and high schools were also asked to increase their presence.

Breaking its silence on the shooting, the National Rifle Association on Friday called for armed police officers in every school. On Wednesday, Gov. Bob McDonnell reportedly said Virginians should “have a discussion about” allowing teachers, principals and other school staff to be armed on campus.

Responding to the governor, the Virginia associations of Secondary School Principals, Elementary Schools Principals and School Superintendents expressed willingness to “participate in any discussion that has the potential to make our schools safer places,” but also concern with the governor’s suggestion.

The problem is “more complex” and the discussion needs to canvas “other and more diverse solutions beginning with defining the roles of School Resource Officers and assistant principals” and restoring state funding for both positions, the associations wrote in a joint news release.

“We cannot and should not turn our schools into fortresses,” Virginia Association of School Superintendents President Ben Kiser stated in the release. “Effective prevention cannot wait until there is a gunman in a school parking lot.”

After Monday’s Suffolk Public Schools cabinet meeting, a memorandum to principals laid out 20 points that “administrative staff must address … with all staff members,” including reviewing safety procedures in school crisis plans and reminding staff to be “aware of their environment and any possible dangers.”

Last week, as instructed by principals, teachers were noting the two nearest exits to their classrooms, being more mindful to always wear their identification badges in full view, and configuring classroom doors to lock automatically on swinging shut to “expedite lockdown procedures.”

Teachers have been instructed to shut and lock windows and doors when classrooms are vacant, reminded of Code Red procedures and asked to provide substitute teachers with safety instructions such as class rolls, emergency codes and evacuation routes.

For principals themselves, instructions include limiting leave from buildings by administrative staff as much as possible, ensuring duty stations are covered and being vigilant that all visitors sign in and wear guest badges.

In a letter sent to parents Tuesday, district Superintendent Deran Whitney stated, “While no amount of planning can guarantee that a tragedy such as this will not occur, we remain vigilant in our efforts to keep staff and students safe while at school.”

The letter was read aloud during a candlelight vigil at Southwestern Elementary Wednesday to honor the 26 school shooting victims. Almost 60 Suffolk Public Schools parents and children joined together in prayers and quiet reflection.

“I think as a nation now, we need to support each other,” one parent said. “We need to come together … to let them know that we do care and we do support them, no matter how far away they are.”