Mr Newman said the emails, some which were sent to 208 unique email addresses, were considered "jokes".
"I have no doubt there are people in all walks of life that would've had jokes similar to the ones Peter had on his computer, on their computer in those days.
"I'm not saying that's okay...in those days they weren't looked upon as anything wrong with them, we have learned since then and yes they are inappropriate."
Mr Witana had been principal of Kawakawa Primary School since 1994.
He was placed on discretionary leave in June 2014 after a document from an unnamed person alleged Mr Witana had mismanaged school finances. It was later found that he was using school finances for personal use, and repaying the money.
When Mr Witana was advised of the complaint, he asked if he could delete certain material off his computer and that he had some inappropriate images on there, the tribunal said.
Subsequently auditors from PWC found the emails containing pornographic material. Some were classed as "hard-core" and "objectionable" images that were likely to be found illegal under the Films, Videos and Publications Classifications Act.
The tribunal said there was no evidence that Mr Witana had searched websites for the images but received and retained the images on four-school devices his emails were synchronised to.
Mr Newman believed the emails were sent and received over a 19-year period.
In the tribunal's decision it said Mr Witana said since his daughters had grown into young women he started to see things differently and said the material was disrespectful to women and men.
PWC's audit also led to information forwarded to police.
As a result former school administrator Nisha Marsh was sentenced to eight months' home detention and 140 hours' community work in June last year after pleading guilty to 13 charges of using a document to gain a pecuniary advantage and five of theft by a person in a special relationship.
Her offending began in December 2012 and lasted just over 11 months, during which time she took $30,980.
The tribunal found that Mr Witana used school funds for personal purchases such as a school pies, his children's stationery or petrol - including petrol cards that he issued to his wife and his mother.
These purchases were documented in the "yellow book" and were always paid back by the end of each year, but in 2013 he let the debt reach $10,084 before he repaid it - this was considered serious misconduct.
Mr Witana also issued petrol cards to some staff, but required them to repay personal purchases within 24 hours of receiving monthly accounts.
In addition to this, the tribunal found the practice of pre-signing of blank cheques exposed the school to the risk of loss of money and he should have taken more care.
Mr Witana has been ordered to tell any prospective employer in the next two years of the tribunal's decision, and cannot hold a position of leadership or financial responsibility until he has satisfied the manager of teacher practice "that he understands the responsibilities of a principal and accounting for funds".