MURFREESBORO, Tenn. -- Authorities at Middle Tennessee State University are investigating a rape at a campus fraternity house.

An underage girl was attending a Halloween party at the Sigma Nu house Saturday night when she was sexually assaulted, said campus police.

The chief of campus police said the woman knew her attacker.

The alleged attacker is not currently a student at the university. Campus police aren't releasing his name until they make the arrest.