MARTIN COUNTY — For the second time this school year, a Martin County student has been charged with making a threat to commit gun violence on a campus, the Sheriff's Office said Saturday.

A threat was posted on Snapchat by a 13-year-old Stuart Middle School student, Sheriff's spokeswoman Christine Weiss said. Authorities learned of the threat Friday night.

Detectives talked with the teen, who lives in Port St. Lucie. At first, he denied posting the threat, which advised students to not forget to bring their guns to school Tuesday, Weiss said. A follow-up post stated that "an AK-47 will do," she said.

The teen blamed his friends for the posts and said he had shared his password with them, he told the Sheriff's Office. Later, he confessed to posting the messages as a joke.

"It's important to tell kids there's nothing funny about this," Weiss said. "Nobody's laughing. You cause pain, fear and concern, and you will face an arrest and a lot of trouble."

The 13-year-old was charged with a felony for making a threat to conduct a mass shooting or an act of terrorism. He was being held at the St. Lucie Regional Juvenile Detention Center in Fort Pierce.

No weapons were found in the boy's home, Weiss said.

An automated call was made to parents Saturday morning about the threat and the boy's arrest.

In late August, the Sheriff's Office charged a 13-year-old Murray Middle School student with written threats to kill. He posted the threat on social media to bring a gun to school. The threat spread to the point it generated about 100 calls to 911.

TCPalm and Treasure Coast Newspapers customarily does not name juveniles accused of crimes, but does name some juveniles depending on the seriousness of the crime, their age, aggravating circumstances and other factors.

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Stancil is a breaking news reporter for FLORIDA TODAY and TCPalm.

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