DENVER -- A former high school band teacher was sentenced Tuesday to prison for 15 years to life for sexually assaulting a 16-year-old female student.

Bailey resident William Robert Eisenman was found guilty at trial in June of sexual assault of a child by one in a position of trust, pattern of conduct, and providing alcohol to a minor.

Addressing the defendant at sentencing, Judge Tamara Russell said, "We send our children to school to be safe. You were there to protect your students and you preyed on them."

Eisenman, 33, was teaching band and orchestra at Evergreen High School in the winter and spring of 2007 when a female student approached him for advice about boys and relationships.

Eisenman developed friendly relationships with many of the students and often acted as their confidant. Many students considered him their friend as well as their teacher, prosecutors said.

When asked for advice about relationships, Eisenman suggested to this 16-year-old student that she dress and act more provocatively to attract boys. He also offered to let her model clothing for him and help her change her image, said David F. Dechant, spokesman for the Jefferson County District Attorney's Office.

Investigators said Eisenman registered at a hotel room in March 2007 and drove the girl there so that she could model the clothing for him. Eisenman sexually assaulted the teen for the first time at the hotel, prosecutors said.

Over the next two months, he continued to sexually assault the teen at the school, in his car, in hotels and at his home, he said.

During a jazz festival in Greeley, Eisenman invited a friend of his to the hotel to have a "threesome" with the teen, Dechant said.

During the trial, prosecutors showed the jurors how Eisenman had groomed the teen, starting with being a good listener and friend. But as their relationship grew, he told her that he had a heart condition that was incurable and that he would die within two to three years.

Eisenman told the girl that he was glad he could talk to her because he couldn't tell his wife about his heart condition because it would upset her, Dechant said.

Eisenman also asked the teen to take care of his wife when he died, Dechant said.