Detective Senior Sergeant Greg Turner, who is in charge of the investigation, yesterday confirmed the vandals are now being sought as the prime suspects. 

He said: “I believe the person responsible for the damage at the college is responsible for the equally violent attack on Karen. Our investigation is focusing on locating the weapon used to puncture 18 reinforced glass windows at the college. We believe it was used to inflict Ms Aim’s severe head injuries.

“We’ve had three days for the people responsible for this damage to approach us. The longer these people are at large, the more suspicious it looks.”

Ms Aim had been travelling around New Zealand for the second time, having fallen in love with the country on her first visit in 2006. 

She was found lying bloodied and barely conscious at 2am on Thursday by police, who had been investigating the break-in at Nui-A-Ti College. She was less than 50 metres from the flat she shared with two friends.

Ms Aim had spent the evening out with a group of friends in the quiet tourist town, which sits on the giant Lake Taupo and is the gateway to the famous volcanic region where the Lord Of The Rings movies were filmed.

However, despite the fact she had been seen in several of the small town’s bars, friends said she was not drunk. On Friday, police released CCTV footage which showed her at a service station half an hour before she was found.

A team of more than 50 uniformed officers have carried out a fingertip search of the area in a bid to find the murder weapon, and detectives now plan to call in specialist divers to trawl through the nearby Waikato River.

Forensic tests are being carried out to establish if she was attacked where she was found or whether she was trying to stagger to the flat for help, and police have been questioning taxi drivers and delivery men who may have been in the area at the time of the incident.

Meanwhile, shocked residents have been asked to carry out searches of their homes and gardens for the weapon or dumped blood-stained clothes.

Police said robbery had been ruled out as a motive since Ms Aim still had her purse and mobile phone when she was found and a post-mortem has shown no signs of sexual assault. 

Mr Turner said: “I have described it as a frenzied attack. It would have created considerable noise and would have taken some time.”

His colleague, Sergeant Tony Jeurissen, who has been with the Taupo murder squad for more than 20 years, said: “This is our first murder in the town for more than a year, and I have never faced such a tragic death.”

Since her death, friends and fellow travellers have left hundreds of tributes on the social networking website Bebo, which Ms Aim often updated with 

stories and pictures of her travels.

Flowers and messages of condolence continued to be left at the scene of the tragedy yesterday.

Tributes were also added to her webpage, although one respondent, calling himself Tame Iti, has been reported to police for an inappropriate post. It included the bizarre statement: “Just like the recent case of the paedophile murdered by the parents of one of his victims in New Zealand, maybe this is a reminder you cannot get away from your evil sins.”

Meanwhile police, who last night said a “number of items” had been found near the scene, also hope DNA tests taken from Ms Aim will throw up clues to her killers.

Senior Sergeant  Jeurissen said: “We took DNA samples, but it’s too early to tell [the results]. Luminol, chemical treatment, was used in a wide area (around the crime scene) to identify invisible blood staining.”