Avondale police arrested Agua Fria High School's special education department chairman Monday on suspicion of raping a 15-year-old female student, authorities said.

Brian Willner, 35, was booked into the Fourth Avenue Jail on one count each of sexual assault and sexual abuse of a minor. He was arrested at his Litchfield Park home at 1:15 p.m., Avondale police spokesman Rueben Gonzales said.

The girl, a special education student, told her mom on April 16 that Willner raped her at the Avondale school a few weeks earlier, according to an Avondale police report. The report gives the following account:

Willner excused the girl from class and brought her into his office. He grabbed her by the arms and took her to the ground. She told officers "she was unable to defend herself because she was not strong enough" and "she felt a lot of pain."

The girl confronted Willner about the alleged rape. He threatened to "kill" her mother if she told anyone what happened.

Once her mom found out, she brought her daughter to Banner Boswell Medical Center in Sun City and called police. A nurse examined the girl and found evidence of rape through internal bruising and cuts. She also tested positive for Chlamydia.

Interviewed at the police station, Willner denied raping the girl. He volunteered to a "computer voice stress analysis test," which showed "deception with answers pertaining to" the rape accusations, the report states.

Investigators obtained a court order to test Willner for Chlamydia, which came back positive Monday.

The girl "suffers" from bipolar disorder, psychosis and ADHD, according to the police report. Police believe the alleged rape was a one-time occurrence, but are looking into the possibility of additional victims.

Dennis Runyan, superintendent of the Agua Fria Union High School District, told The Arizona Republic on Monday afternoon that Willner had been on paid leave from the school, 530 E. Riley Drive, since police "requested an opportunity to speak with him" Friday.

District and school officials said they'll cooperate fully with police during the investigation. Runyan said a letter will be sent home to parents Tuesday.

"The school has made appropriate arrangements to cover the teacher's classes and other professional responsibilities," Runyan wrote in a statement Monday. "Our Number One priority is always the safety of all of our students."

Willner started his career in the Litchfield Elementary School District in 2002 and worked in special education programs at Verrado Elementary School in Buckeye and White Tanks Learning Center near Buckeye.

"I thought he always made decisions in the best interests of our kids. He was a good employee," said Heather Cruz, Litchfield's assistant superintendent, who was Verrado Elementary School's principal while Willner worked there.

Willner left Litchfield in 2008 because of "other opportunities," according to his resignation letter obtained by The Republic.

Agua Fria High School Principal Matt Smith hired Willner in 2008.