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

NIU spokesman Joe King said authorities were at the station, but he declined to elaborate. 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.

The university fired police chief Donald Grady from his $200,000-a-year job on Feb. 19, saying he mishandled evidence in an investigation into allegations that a campus police officer had sexually assaulted a student in October 2011. A DeKalb County grand jury indicted the 25-year-old former police officer, Andrew Rifkin, later in February.

As Wednesday's raid began, the FBI went out of its way to note it "is not in response to any public safety concerns" — apparently an effort to allay any anxieties among faculty and the 25,000 students at NIU, where a gunman killed five students in a lecture hall in 2008.

The 6-foot-5, tough-talking Grady was hailed as a hero for sprinting from the police station and into the nearby NIU classroom during the Feb. 14, 2008, shooting. When they arrived, gunman Steven Kazmierczak had already committed suicide. But survivors praised Grady for his bravery.

Grady's Madison, Wis.-based attorney, Michael Fox, said in a phone interview Wednesday that an investigation the chief launched into an off-the-books repository for proceeds from the sale of university-owned scrap metal may have contributed to his dismissal. Fox said eight NIU employees and one former employee were criminally charged last year.

However, Fox had no information on the FBI raid, saying it could be related to Rifkin or the scrap-metal investigation, or something entirely different.

"Without equivocation, he (Grady) denies wrongdoing in any of these matters," Fox said.

Fox added that he didn't believe Grady's handling of the sexual assault case was the sole factor in his firing and that it could have been "retribution" for his investigation into the scrap-metal scheme.

While Grady gained admirers, others criticized him as combative and uncooperative. In 2009, he was put on paid leave after an editor of the campus newspaper accused him of threatening and shouting at him during an interview. He was later cleared of wrongdoing and reinstated.

A message left at a residential number for Grady wasn't returned Wednesday.

Rifkin's attorney, Bruce Brandwein, said he had been in court when the Wednesday morning raid took place and couldn't immediately say if it was connected to his client's case. He did say Rifkin intends to enter a not guilty plea to the sexual assault charges.

"He absolutely denies any wrongdoing," Brandwein said.

Adding another layer to Rifkin's case is a civil lawsuit he filed earlier this year.

The suit, first filed in state court and then moved to U.S. District Court, names NIU, Grady and other NIU officers as plaintiffs. It alleges Rifkin was tricked by NIU officers into signing a confession regarding the alleged sexual assault. It also alleges witness statements that might have cleared him weren't forwarded to investigators.

All the plaintiffs have denied any wrongdoing.