Federal prosecutors have joined an investigation of a racist incident on the campus of American University.

Last week, someone hung bananas with racist messages from nooses at several locations around the campus. The bananas were found shortly after Taylor Dumpson became the first black woman to serve as AU's student body president.

AU president Neil Kerwin revealed in a letter to students and staff on Wednesday that the U.S. Attorney's Office for the District of Columbia is now involved in the probe. The FBI had already been assisting campus police in the investigation.

Authorities have released video of a person of interest, but no arrests have been made.

The university also provided extra security to Dumpson after a post on a white supremacist website asked people to harass her.