Police are hoping holidaymakers' photos provide the key to finding who stabbed a tourist in the head at Waihi Beach.
The 64-year-old expat who now lives in Queensland is in a critical condition in Waikato Hospital's Intensive Car Unit with severe head injuries after the New Year's Day attack.
The man and his wife were staying in a caravan in front of a friend's house when the attack happened.
Police were trying to speak to as many people in the area as possible in the area before holidaymakers head home but stopping cars as they left caused too much congestion.
They are now turning their attention to holiday pictures to solve the case.
"People often take snaps of New Year's Eve revellers and then think nothing more of them. What we are after is images of people in and around Beach, Hinemoa and Ocean View Roads, the surf club, camping ground and Esplanade between 12.30am and 1.30am," Inspector Dana McDonald said.
"During that time lines of police were ushering large numbers of people out of the area, trying to encourage them to go home and we feel there may be dozens of potentially very useful images out there."
Twenty officers were working on the case and he said it was likely more would be drafted in over the next few days.
The attack happened at about 1am on January 1, and there were a lot of people nearby.
Anyone with such images is asked to email them to Thames@police.govt.nz along with consent the images may be used by NZ Police and also the names of any people identifiable in the images.
McDonald called it a tragedy for the family of the victim and the wider Waihi Beach community and appealed for anyone with information to come forward.
McDonald also had a warning for the offender.
"By now the seriousness of the situation has more than likely become apparent to anyone involved," he said.
"Our advice to that person, or those persons involved, is that the situation is not going to get any better without them making contact with us. We would advise you to do the right thing and make contact with police rather than wait for us to find you."
Anyone who has any information can contact police on 07 858 6200 or Crimestoppers anonymously on 0800 555111.