Three students were arrested Thursday in connection with graffiti at their high school in Howard County, Md., that included a swastika and a racial slur, police said.

Students preparing for an end-of-year senior ceremony Thursday morning at Glenelg High School discovered the vandalism, which Howard schools Superintendent Michael J. Martirano called “hateful and sickening.”

“Make no mistake, this is a hate crime against so many of our communities,” Martirano said in a statement. “It is completely unacceptable and actions of this nature will not be tolerated in Howard County.”

Sherry Llewellyn, a spokeswoman for Howard police, said the three students who were arrested are over the age of 18. The department has not revealed their names.

Brian Bassett, a spokesman for the Howard County Public Schools, said staff painted over or power-washed the graffiti.

“A sense of normalcy was maintained for students and the graduating seniors were able to have their awards celebration as planned,” Bassett wrote in an email.

Howard County Executive Allan H. Kittleman (R) called the incident an “appalling display of bigotry” at the school his four children attended, and where one of his daughters now teaches.

“We cannot let those who promote hate destroy our important year-end traditions and must remind ourselves that this type of intolerant behavior is the work of a small number of hateful individuals,” Kittleman wrote on Facebook. “They do not represent our shared beliefs as a community.”