PARKLAND, Fla. (AP) — A South Florida teenager has been arrested after investigators learned he made a threat against Marjory Stoneman Douglas High School, the site of a mass shooting that killed 17 people on Valentine’s Day in 2018.

A caller reported seeing the threat late Wednesday night, according to the Broward Sheriff’s Office. Officials said the 17-year-old high school junior had sent a text message to his classmates in a social media chat room just after 9 p.m. Wednesday. The threat came one day after a student allegedly killed four classmates in Michigan.

“I feel like school shooting tmrw (tomorrow). When I sneeze it’s a signal go to the bathroom OK. I hope y’all aren’t snitches,” the text message said, according to a probable cause affidavit.

Investigators found the student at his home, and he was arrested early Thursday on one count of writing a threat to conduct a mass shooting, sheriff’s officials said.

The school’s principal, Michelle Kefford, notified parents about the threat Thursday morning through a robocall. Stoneman Douglas has been at the center of national debate and activism over gun violence in schools since a former student killed 17 people and wounded another 17 in 2018.

The mother of the teen told WSVN that he didn’t mean it, that to him it was a joke. She said that they had lived in another country where schools are safe at the time of the massacre in Parkland. “He’s a normal kid from a normal family and a safe environment. He doesn’t realize the world is not so safe,” she said.

“In my country, schools are very safe. Our mindset is very peaceful. He just wanted to show up among his friends,” she said. “It’s not an excuse for his behavior. It’s just an explanation for his behavior. All threats must be investigated. I understand that.”

Tony Montalto, president of Stand With Parkland, the group that represents the families whose relatives died in the 2018 shooting, said the threat “further proves the need for timely investigation and notification to parents regarding threats to schools.”

“In the wake of the Michigan shootings this week and this incident…, I urge our elected leaders at all levels of government to commit to a renewed focus on the safety of students and staff,” Montalto said.