WEST PALM BEACH, Fla. (WPTV/WFLA) — Investigators in South Florida are trying to figure out who created a note that they say threatened a high school mass shooting.

According to Martin County Sheriff William Snyder, a teacher found the crumpled up note next to her desk last Friday at Jensen Beach High School in West Palm Beach.

Snyder said it was written as a note to self that said to bring a gun to the school on Sept. 8, for the person’s intended targets. It then listed nine names of students at the school.

“It’s pretty blunt. It’s pretty graphic. It doesn’t leave anything to the imagination. There’s nothing to interpret. It’s just flat out threat to bring a gun to school and to shoot nine students,” he said.

According to our NBC affiliate, WPTV, deputies don’t know who wrote the note, however, say they do have several leads.

“We’re treating it 100% as if it’s a legitimate threat,” Snyder said. “As far as I’m concerned, I have a threat to shoot nine students at one of our schools. And we’re absolutely reacting as if that threat will be carried out.”

The sheriff’s office has tightened security at the high school and will increase the number of school resource officers on campus, WPTV said.