"Our main focus in this investigation is to find Simon whatever the circumstances may be."
He said people involved in Mr Garrick's disappearance may have "got caught up in a situation that's not of their own making and beyond their control, and subsequently shown poor judgement", and appealed for them to come forward.
"Over time allegiances change and I am sure that the knowledge that will enable Simon to be returned to his family, is held by someone in our community," he said.
Mr Garrick was last seen at the Caversham Four Square supermarket in Dunedin on Tuesday, October 30 last year. There has been no activity on his phone or bank accounts since.
Mr Garrick also missed his father's funeral, in December 2012, and police believe they are now investigating a homicide, said Mr Shaw.
Seven detectives have been working on the case, taking their inquiries as far as Australia to try to uncover what happened.
Mr Garrick's case featured on Police Ten 7 last night.