MONROE, Wis. -- A Monroe High School student was taken into custody after a shotgun was discovered in a vehicle in the school's parking lot Monday, police said.

Monroe police said they were investigating a report of a 16-year-old male student possessing a firearm on school grounds when authorities found the shotgun.

Police said the 12-gauge shotgun was located cased and unloaded in a vehicle by school staff. Police said the firearm was secured by the Monroe officer assigned to patrol the school, and during the course of the investigation, the officer found that the firearm was allegedly stolen from a rural Monroe residence.

Police said the student was taken into custody by Monroe police and later ordered held in secure detention by Juvenile Intake, pending further action.

Authorities said the stolen firearm case was referred to the Green County Sheriff's Department for further investigation.

School authorities said they will investigate any violation of school rules.

Police said the incident doesn't appear to be related to any of the recent school threats or a recent incident of vandalism at Monroe schools.