Two students at Horizon Middle School in Kissimmee, Florida were arrested last week after an investigation found that they were plotting a violent attack at their school, including listing the names of “safe” students, according to Osceola County’s Sheriff’s Office.

According to the press release, the investigation began on Tuesday after deputies were made aware of the list by a student who said they were told by another student they were considered “safe.”

The students, whose names haven’t been released, acknowledged drafting two lists of students, one under a “safe” category and another under a “stab” category, according to the Osceola County Sheriff’s office. The students claimed it was just a joke.

“There was also talk about sneaking a gun into the school and shooting students as well as stabbing them,” said a news release from Osceola County Sheriff’s Office Major Jacob Ruiz. “This caused concern for the students in regards to the possibility that there may be additional information or another list of students that may not be ‘safe’.”

The accused students were charged with making written threats to kill or conduct a mass shooting and are being held in the Orange County Juvenile Detention Center on Bumby Avenue.

On Tuesday, the Florida Department of Juvenile Justice launched an “It’s No Joke” awareness campaign as students getting charged with school threat offenses increased in Florida the last three years.

“There is nothing funny about threatening a school, and there is nothing funny about being charged with a felony,” Juvenile Justice Secretary Simone Marstiller said in a statement. “We want young people thing twice before casually threatening violence in their schools.”