A longtime math professor at the University of Hawai'i sexually assaulted a girl over a six-year period beginning when the girl, described as a family friend, was 7 years old, according to court documents.

David A. Stegenga, 63, was charged yesterday with seven counts of first-degree sexual assault and five counts of third-degree sexual assault. He was released on $500,000 bail yesterday.

Stegenga, of Enchanted Lake in Kailua, was arrested at 10:30 a.m. Thursday on the UH-Manoa campus, where he has taught mathematics since 1980. Court documents characterized Stegenga as a neighbor and family friend of the victim.

But beginning in 1999 when the girl was 7 years old, Stegenga began to regularly sexually assault the girl, according to a police affidavit filed in District Court. The girl told police that he performed sexual acts on her "two to four times a week" until 2005 when the girl was 13 years old.

The alleged assaults occurred in his home, her home, his automobile, Kailua Beach Park and in the home of a neighbor, the affidavit said. When she was 8 or 9, the court document said, Stegenga placed her on his lap, showed her pictures of animals mating and sexually assaulted her.

The victim's older sister also told investigators that she saw naked pictures of herself when she was 12 or 13 on Stegenga's home computer, the affidavit said.

On Sept. 10, a temporary restraining order was filed by the victim and her family against Stegenga and his wife, Bridgit. The order was served to the couple on the day of Stegenga's arrest.

Bridgit Stegenga could not be reached for comment.

Reed Dasenbrock, University of Hawai'i vice chancellor for academic affairs, issued a statement yesterday on the arrest of Stegenga:

"We are concerned about the allegations leading to (Thursday's) arrest of Professor David A. Stegenga, as the safety of our students, faculty and staff is of the highest priority," Dasenbrock said. "We are cooperating fully with the HPD investigation."

Dasenbrock said Stegenga's classes are being covered by other staff members. He said the university declined further comment because the case is a personnel matter.

In addition to his teaching duties, Stegenga is an active member of the Honolulu Zoo Society. He has served as a keeper's helper in the savanna section of the zoo for years and was named "volunteer of the year" in 2007.

Stegenga and his wife created the zoo's Web site, and from 2001 to 2007 he served as vice president of the zoo's board. He was instrumental in the planning and construction of the zoo's tiger exhibit, according the the zoo's Web site.