GREELEY, Colo. -- The president of the University of Northern Colorado on Friday addressed allegations that the university knew for years about a professor's alleged sexual contact with students but did nothing about it.

UNC President Kay Norton confirmed that the university has hired a company to conduct an internal investigation.

"Let me be clear. The University of Northern Colorado has placed no limits on the investigation. We will fully investigate Mr. Fulkerson's conduct, as well as how the university responded to the conduct over the years. We will not shrink from the truth, whatever it may be. Given that we're talking about many years and many people, the truth is likely to be complicated and painful," Norton said. "We cannot change the past but we can and will learn from it."

Music theater professor Raymond Vance Fulkerson , 63, is accused of taping young male students in his bathroom. He was arrested last week and charged this week with sexual exploitation of children, unlawful sexual contact and possession of marijuana.

However, after news of his arrest became public, former students and colleagues told reporters that they went to the school and filed complaints against Fulkerson -- one as early as 1991 -- but nothing was done about it.

Norton said it was too early to tell who knew what and when but said it's possible this investigation can span decades -- perhaps as far back as 1989, when Fulkerson was hired.

Norton said Fulkerson's behavior falls into the realm of sexual harassment, and she is continually surprised and saddened as she learns new information from the investigation.

"Rules and laws about behavior are important but they're not effective if we don't commit to them wholly," she said. "We will improve our rules and processes if need be ... We are going to learn whatever lessons there are in this sad situation."

She said UNC is collecting all available records on Fulkerson.

"This is going to be a process, not an event," Norton said.

Fulkerson is currently on paid administrative leave. He is banned from campus and any further contact with any student.

One of his former students, Christopher Johnson, told the Denver Post that Fulkerson performed a sexual act on him in 1991 but when he filed a written sexual-harassment complaint with the Dean of Music at the time, he received no response.

Other students said that Fulkerson for years had used his position to pressure students into sex, and the theater has a culture of questionable and inappropriate relationships between students and staff.

Norton said the investigation will look into policies governing relationships between students and faculty members.

"This is a great university because of the community we have built based on the commitment to each other. We are responsible for sustaining a healthy campus climate," Norton said.

Fulkerson was arrested after police, acting on a tip from a student, found a wireless video camera hidden on the toilet in his bathroom. The camera, which captured guests urinating or showering, fed directly into a TV in Fulkerson's bedroom. Greeley police said they also found tapes and DVD of the recordings in his bedroom as well as images of nude boys in Fulkerson's locked safe.

Fulkerson faces 18 months in prison and up to $100,000 in fines if convicted.