MUSCLE SHOALS (AP) — Police in Alabama are investigating a note found on the floor of a high school that threatened a shooting on Halloween.

Muscle Shoals City Schools Superintendent Brian Lindsey tells the TimesDaily the note said “The school will be shot up on Halloween day…be ready or don’t show up.” He said Sunday that school officials know who had the note at some point Friday and there is video surveillance, but authorities still are working to determine the origin.

A Sunday letter by the school says officials are interviewing people believed to know about the note. Muscle Shoals police say there will be increased police presence at the school this week. A police department release says all district school campuses are also monitored by live video surveillance feeds linked to police dispatch.