The denials, as well as his high-security status, meant the prisoner could not enter the Child Sex Offender Treatment Programme.
The board heard he had committed two assaults while behind bars, one of which involved a "vicious kicking of another prisoner", Sir Ron said.
In 2014, Witchall met a 16-year-old girl through a mutual friend and tried to hug her as they left.
Her resistance made him angry and he coerced her into going with him into the basement car park.
Despite her attempts to escape, Witchall would not allow her to and said she could only leave after they had sex.
Three of his sexual grooming victims were aged 14, the other 15.
Witchall would persistently message them online and persuade them to meet him until they acquiesced.
One girl he groped in a library aisle before she ran off.
Others he organised to meet in parks or at school grounds where the indecent assaults would inevitably take place.
The lewd misconduct had continued while in prison, the Parole Board heard.
"He has had 10 misconduct charges since he has been in prison, mostly involving violence or aggression and overall he has had very poor conduct. Some of the objectionable conduct includes sexualised conduct," Sir Ron said.
"Currently, it is difficult to see the way forward for him. He is behaving poorly in prison and does not have an immediate and obvious rehabilitative pathway towards release."
A psychologist will provide another report on Witchall before his next parole hearing in August 2021.
This article was first published on the Otago Daily Times.