Bathroom graffiti, Snapchat threats made against Forest Park High School in Prince William County

WOODBRIDGE, Va. - Officials in Prince William County are taking extra precautions after multiple threats have been reported against Forest Park High School in Woodbridge.

There was a visible police presence at the high school on Friday after a threat appeared on Snapchat showing a doctored school calendar indicating a school shooting would take place on March 12. Police and school administration say the threat is under investigation.

Last week, there was an incident involving graffiti written on a bathroom wall containing a message warning of a threat to the school -- also for March 12.

A letter went home to parents Friday informing them about the recent threats and what is taking place to protect students. An additional police presence will be on campus on Monday before, during and after school, school officials say.

The letter from Forest Park principal Richard Martinez said:

Dear Forest Park High School Parents and Guardians:

The purpose of this communication is to share two pieces of information, one regarding an unplanned event which occurred today and another incident that was brought to our attention regarding a posting on social media.

This afternoon, everyone briefly evacuated the building due to a fire alarm. It has been determined that it was a false alarm. Everyone is safe and we will be working to determine who pulled the fire alarm and caused this disruption to our school day.

The other matter is in reference to the information shared last week with regarding someone who had written graffiti on a bathroom wall with a warning about a threat to our school on March 12, 2018. The matter was reported to the Prince William Police Department and PWCS Risk Management Office. The Police continue to investigate.

I want to share with you that it was brought to our attention this afternoon that someone posted something on Snapchat that purportedly indicated that the same threat was posted on the PWCS website. We cannot confirm that this threat was posted on the PWCS website, and the Snapchat posting is gone. We continue to investigate.

Please be assured that on March 12, as a precautionary measure, the Prince William County Police Department will have additional officers on hand at arrival, throughout the day, especially during lunch periods, and during dismissal.

We take this matter very seriously and are committed to ensuring a safe and secure environment at our school. The safety of our students and staff is our number one priority. We recognize our students and parents who contact administration to support our stance of, "see something, say something." With everyone's help, we can continue to keep our school a safe and effective place to learn.

Understandably, students and families are concerned about safety.

Police said they have investigated multiple threats since the school shooting in Florida, but none of them have been deemed credible.

We are told a handful of students have been arrested and charged for making threats, although their cases are unrelated. Police said in each circumstance, the accused students said the threat was a joke, they were trying to impress someone or other reasons.