Hateful messages were spray-painted on a shed at Walt Whitman High School in Bethesda, Maryland.
Margaret Oleynik told News4 she was driving through the school parking lot when she discovered the vandalism Friday night.
"Something very racist, very not OK in a very white neighborhood. There's not a lot of color around here and it's very … insulting," Oleynik said.
Using yellow spray paint, someone wrote a racial slur, the word "lynch" and drew a noose on a shed outside the school.
Oleynik posted the photos on social media and told the police. She said she feels the timing of the vandalism is particularly hurtful as many are supporting the Black Lives Matter movement.
"It broke my heart, honestly. I didn't think that people around here were like that. But, apparently, they are and I could never understand how someone could do that," she said.
The school's principal sent a letter to the community condemning the graffiti. A similar incident happened at the school in February.
"If it is discovered that our students were involved, they will receive serious consequences and may face additional charges from Montgomery County Police," Principal Robert Dodd said.
"I feel both outrage and deep grief that acts of racism and hate continue to occur at Walt Whitman."