CHICAGO (AP) — The FBI searched the campus police station at Northern Illinois University for at least eight hours on Wednesday, weeks after a former NIU police officer was indicted on sexual assault charges and the department's longtime police chief was fired.

By the end of the day, however, there was no official word about why federal authorities raided the tiny building at the heart of the 25,000-student campus sometime before 8:00 a.m. and stayed late into the afternoon.

FBI spokeswoman Joan Hyde said only that search warrants were executed on campus in "an ongoing criminal investigation" involving Illinois State Police, the U.S. Department of Education and U.S. Department of Housing and Urban Development.