The investigation began in May 2016, after a former student contacted the district, saying Johnson abused him while he was a student.
Johnson taught at the school from 1958 to 1991.
In all, the district spoke to 12 former students who claim Johnson abused them. District Superintendent Robert Kobylski said the students all had similar stories.
"The District believes that going forward, our energy and resources would be best used to focus on assisting Mr. Johnson's victims and protecting current and future students of Nicolet High School," said Kobylski. "At the same time, by leaving the matter open, we can send a signal to any other victims that we remain supportive, willing and able to be helpful to anyone who might come forward in the future."
The District is working with Aurora Health and its Healing Centers to provide support to any of Johnson's victims at no cost.
Johnson committed suicide in his Waupaca home shortly after the abuse claims became public.