Administrators at Riverwood International Charter School in Sandy Springs are examining security procedures after the arrests of four “intruders” Friday.

In a letter sent to parents, Principal Robert Shaw said students noticed two men walking in the hallways and told school staff. When staff confronted the men, they said they were looking for a student who had sold their sister a fake ID, the principal’s letter says.

“Upon questioning the individuals, we learned that there were two other young men in a car waiting outside of the school,” the letter says. “All four of the individuals were questioned by our school resource officer as well as the Sandy Springs Police Department. During a search of the car, marijuana and a BB gun were found.”

Patch.com reports that the men were arrested.

Shaw thanked the students who reported the incident and said he is trying to determine how the men got on campus.

“The most important part of all of our safety protocols is the work we do building relationships with students so they feel comfortable telling us when there are problems,” his letter says.  “This is a serious situation and I am committed to finding answers.”