Detective Inspector Chris Page of the Waikato CIB said more than 30 police from Waikato, Counties Manukau, Auckland and the Bay of Plenty were now working on the investigation, dubbed Operation Brad.
"In addition to that, officers who had been engaged on the area canvas are now carrying out various area searches as we seek to identify and locate the object used to cause Mr Wilkinson's injuries," Mr Page said.
Last night, police again appealed to New Year's revellers in the area at the time of the attack to email them any photographs taken in the area that night.
This was not necessarily to target the person whose picture was being taken but the strangers in the background or off to the sides of the shot.
If anyone had such photographs, they were asked to send them in, including the names of anyone who could be identified.
Mr Page also appealed to the offender and their friends to come forward.
"This matter is now a homicide investigation and can be resolved by the persons involved making contact with us or our team locating them. We ask that if you know who was involved or were involved you make contact with police."
To provide information call (07) 858 6200, or call Crimestoppers anonymously on 0800 555 111. Photographs can be sent to thames@police.govt.nz
