MIDDLETON, Wis. – After a four-year investigation, the Wisconsin Department of Public Instruction has determined a teacher caught viewing pornography on school computers can keep his teaching license.

The ruling comes despite Gov. Scott Walker’s call for the department to permanently revoke his license.

Middleton science teacher Andrew Harris was fired from his job in 2009 after a colleague reported to school officials that the teacher was viewing inappropriate pornographic images on his school computer.

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A school district investigation found Harris viewed nude images contained in 23 emails from his sister over the course of several years, and that other teachers in the district had also viewed or shared inappropriate material, the Wisconsin State Journal reports.

Harris filed a union grievance over his termination through the state’s appeal process for tenured teachers, and an arbitrator in 2012 ruled Harris must be reinstated to his job. The Middleton-Cross Plains school district spent four years and nearly $1 million to fight the arbitrator’s ruling through the court system, but was unsuccessful in getting the decision reversed, according to media reports.

The district also asked the state Department of Public Instruction to revoke Harris’ teaching license in 2010. DPI officials allegedly conducted a four-year investigation into the case, and Walker pressured the department to follow through with a revocation when Harris was returned to the classroom in January of this year.

The case convinced Wisconsin lawmakers in 2011 to pass legislation that criminalizes viewing pornography on taxpayer-owned computers, but DPI officials contend Harris did not violate the law as written at the time and doesn’t deserve to lose his job.

“While your conduct certainly was highly inappropriate for an educator, it does not meet the legal definition of immoral conduct contained in the 2008-09 law,” according to a letter sent to Harris by DPI, the Journal reports. “Specifically, the Department’s investigation confirmed the school district’s public statements that your conduct did not involve children in any manner.”

Walker and Middleton-Cross Plains officials were not pleased with DPI’s decision.

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“We believe the Department of Public Instruction does indeed have the legal authority to revoke his license under prior law, and Gov. Walker thinks they should do so,” Walker spokeswoman Laurel Patrick told the news site.

“The (school board) took a stand against viewing pornography in school and requested a review of this case four years ago. Our state superintendent clearly doesn’t believe viewing pornography in school over a long period of time justifies license revocation,” district spokesman Perry Hibner said in a prepared statement.

“Thankfully, the Legislature clarified this law to make certain that no other school district will have to deal with a similar case again. Our school district is abiding by the ruling of the arbitrator, and will provide the best possible environment for our students and our employees,” he said.