"We just wish that we could change over, instead of this absolute nightmare that we're going through."
Mr Aim, a self-employed builder and joiner in Orkney, said the last time he and wife Peggy saw Karen was when they dropped her off at an airport last October.
"When we said goodbye I never thought that would be the last time we would see our beautiful girl again. It is still too hard to take in. There have been so many tears."
Mr Aim said police woke him at 4.30am on Thursday to break the news.
"It's all still like a bad dream," he said. "I thought I would find my son Alan locked out after a night out - instead it was the police there to tell me Karen had been murdered."
Miss Aim died from severe injuries 50 metres from the flat she shared with friends.
Police in Taupo believe the person or people who attacked her are the same people who vandalised windows at Taupo-Nui-A-Tui College. They also believe the same weapon was used, though they have not revealed what that is.
Inquiry head Detective Sergeant Greg Turner said yesterday that a criminal profiling team from Auckland had begun work to help detectives find a motive for the brutal slaying. Robbery and sexual motives have been ruled out.
Mr Turner admitted they might never find a motive - but said they would find the murderer.
"We are doing the hard yards and we will find the person or people behind this."
Cordons at the school and surrounding streets were lifted yesterday after an extensive search by forensic specialists.
Police are also to investigate offensive website postings on Ms Aim's Bebo site.
Mr Turner said police wanted to establish whether the writer was "someone with mental issues" or someone connected to the murder.
- ADDITIONAL REPORTING BY AGENCIES