Nassau Police Commissioner Patrick Ryder speaks in Mineola on March...

Nassau Police Commissioner Patrick Ryder speaks in Mineola on March 5, 2018. Credit: Howard Schnapp

Nassau County police identified and were investigating the source of a Snapchat post Monday that affected Long Island school districts, generating scores of calls to law enforcement officials and prompting heightened security and some campus lockdowns.

The person was being investigated by other agencies, a law enforcement source said. It was not immediately clear if the person was in custody.

In addition, Suffolk County police said they were “investigating circumstances surrounding a Snapchat photo that threatened school violence. No specific school was named. A preliminary investigation determined the photo was not posted by anyone in Suffolk County.”

A law enforcement source familiar with the threat said one Snapchat post went viral and confirmed it included a drawing of a mermaid.

Nassau Police Commissioner Patrick Ryder, in a statement, said the department will charge anyone who makes threats to schools in the county with making a terroristic threat — a Class D felony punishable by up to seven years in prison.

The commissioner’s statement came following a smattering of reports from school systems in both Nassau and Suffolk counties about threatening posts on social media. Some districts put schools on lockdown.

“I would like to assure all Nassau County residents, school personnel and students that all threats received by the Police Department are taken seriously until they are deemed unfounded or noncredible,” Ryder said in the statement. “Numerous investigative resources are expended during these investigations and false threats will never be tolerated.”

He said the county “has experienced a large influx of threats of violence to schools” since the Feb. 14 mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, in which 17 students and faculty members were killed.

On the East End, the Southampton Town Police Department added one officer to each of the high schools in the Southampton, Bridgehampton and Hampton Bays school districts after school officials alerted the agency before noon Monday to a Snapchat threat that had been circulating throughout Suffolk County, Southampton Lt. Susan Ralph said in an interview.

“We don’t know if it’s a copycat or someone crying out for attention,” Ralph said. “Our job is to provide the utmost protection for the school districts, as well as the children and the teachers and the staff.”

Lars Clemensen, president of the Suffolk County School Superintendents Association, sent a letter to Suffolk residents addressing the social media threats and noted that multiple superintendents had alerted the Suffolk police department about the postings.

“It is unfortunate that recent events have caused an increase in this type of ‘copycat’ posts, which tend to cause a significant disruption in the learning environment,” Clemensen wrote. “We truly understand that the latest incidents across the country have brought increased awareness on the safety and security of our school buildings. Please know that every precaution is taken on a daily basis to protect the safety of our students and staff and to provide a secure learning environment for all.”

In the Central Islip school district, there was “increased Suffolk County police presence” and “heightened district security protocols” at schools after administrators learned of “a viral unspecific social media threat against schools that has been circulating,” according to a posting on the district’s website Monday.

In the Sayville district, school officials on Sunday alerted parents of a “school threat that was posted on social media,” according to a posting on the district’s website from Superintendent John E. Stimmel, who noted that “the post was vague and we were given reason to believe that it was not directed towards Sayville.”

Stimmel’s posting, updated Sunday night, noted the district became “aware of another posting (probably not related to the first post) threatening violence in Sayville” that contained “few details.” The notice stated that “we have precautions in place and there will be an increased presence of police in the district.”

In the North Shore school district in Nassau County, a lockdown occurred Monday at the system’s schools after police responded to a parent’s call of a rumor of a possible threat, a police spokesman said. The spokesman said there was “no direct or indirect threat made.”

At Valley Stream Central High School, some students received anonymous messages Monday involving threats. That incident remained under investigation. The spokesman said police also had investigated a threat to the high school on Sunday night, and it was determined not to be credible.

On Friday, a student was arrested for making a threat to Farmingdale High School, a Nassau police spokesman said. It involved a statement made from one student to another, the spokesman said.

Youssef Mohammed, 17, of South Farmingdale, was charged with making a terroristic threat and arraigned Saturday, Nassau police said. Bail was set at $15,000.

With Ellen Yan

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