LOS ANGELES, Jan. 19 (UPI) -- Dozens of schools over six states were evacuated Tuesday after callers or emails threatened to shoot or bomb students and staff, police said.
Threats came to individual schools in Delaware, Iowa, Maryland, Massachusetts, New Jersey and Pennsylvania and were the latest in weeks of threats affecting schools in the United States.
No credible threats have been found, but the steady flow of disruption and alarm has cost school districts time and money, and stirred anxiety about possible terrorist attacks.
The problem might has started in December when Los Angeles Unified School District, the second largest in the country, was forced to close all of its more than 900 schools after a threatening email.
Threats have often come in the form of a computer-generated robocall, officials told NBC. Some of which were routed through Bakersfield, California.
The technology mostly used by telemarketers and political campaigns is easily accessible through websites that offer the services for less than a penny a minute.
Police in New Jersey said they were taking "all precautions" to "ensure safety" and closed various schools before taking bomb-sniffing dogs through campuses, even though they did not believe the threat was real.
Police and school staff in Massachusetts faced the same challenges.
"This threat appears to be part of a widespread issue that affected multiple school districts across the state over the past two weeks," Arlington High School Superintendent Kathleen Bodie said in a statement. "Despite the fact that this was a widespread issue, we take these threats very seriously. Given the police presence and investigation, and out of an abundance of caution, we decided it would be in our best interests to release students, faculty and staff for the day. This also prevented students and staff from having to stand outside in the cold while police conducted a sweep of the building.
Bradley Stein, a child and adolescent psychiatrist at RAND said even unfounded threats can affect people. "These threats create anxiety in students and in their parents," and the effects can linger long after the threat has passed, Stein said. "It raises the possibility that schools may not be safe."