WOODBRIDGE, Va. — A Virginia high school principal says extra police will be on scene at his high school on Monday after graffiti was found that threatened a school shooting.

WTTG-TV cites a letter from Forest Park High School principal Richard Martinez that says graffiti on a bathroom wall said a shooting would take place at the Woodbridge, Virginia, school Monday. Martinez says this discovery followed reports of the threat being posted to Snapchat and the Prince William County Public Schools website , though he notes neither of these online threats have been confirmed.

The principal says in the Friday letter that extra officers from the Prince William Police Department will be at the school Monday before, during and after classes as a precaution. He also says school officials and police are investigating.

Information from: WTTG-TV, http://www.myfoxdc.com