Officials at Montclair State University said they are investigating a bias incident in which someone drew a picture of planes hitting the World Trade Center on the door of a Muslim student group’s headquarters, according to a report on NJ.com.

Campus spokeswoman Suzanne Bronski said the graffiti was found Monday, Feb. 4 on the door of the Office of the Muslim Student Association located in the student center, the report said.

School officials are treating the incident as a crime and university police and the university’s Bias Response Team are investigating.

In 2011 and 2012, graffiti and notes with anti-gay messages were discovered in and near the school’s Lesbian, Gay, Bisexual and Transgender Center, school official said.