The parents of Christie Marceau, who was stabbed to death by Akshay Chand in 2011, fear he could strike again and want notification next time he is on escorted leave.
Chand has been a special patient of the Mason Clinic under mental health legislation since he was found not guilty of the teenager's murder by reason of insanity.
Brian and Tracey Marceau, who no longer live in New Zealand, were told on Tuesday that Chand had been seen at public places in Auckland including a library, McDonald's and a Countdown supermarket.
They had not been notified by Waitemata District Health Board, which runs the clinic.
The Marceaus told the Herald they were afraid Chand would be able to harm their remaining family in Auckland, or other members of the public.
"He is a ticking time bomb and knows how to deceive and manipulate to get freedom. He has stated before that he hasn't finished and this is incredibly frightening."
Chand killed Christie in her own home while on bail for earlier offending against the 18-year-old, including kidnap and assault.
The Marceaus, who have another daughter, Heather, said they couldn't believe it when they were told Chand had been allowed out on escorted leave.
"... and that authorities could be so reckless and have little consideration for us, our family and friends and public safety. It has distressed us immensely and we are struggling to cope."
They said there were extremely concerned Chand, who was diagnosed with paranoid schizophrenia, would have the opportunity to reoffend.
"If they [our family] were in the same vicinity without knowing we do not know if this would be a trigger.
"We were led to believe by leading psychologists at the hearing five years ago that his prognosis for recovery was very poor due to the condition coming on at a young age and its rapid onset."
The couple said they wanted to see amendments to the Victims Rights Act to prevent this happening to other families.
"Victims of mental health offenders must be kept safe and treated with respect, they do not choose to be in that position."
They called for the mental health system to "stop hiding behind bureaucracy".
"They know it's wrong or they wouldn't try to cover it up and keep his public outings secret."
Their victim advocate, Ruth Money, claimed Waitemata DHB had misled the public about a loophole in the Act which meant they did not have to legally inform the family when Chand was on escorted leave, only unescorted leave.
"The Mason Clinic is simply using semantics as there is no limitation to stop them telling us about the escorted leave as they are claiming."
The DHB reportedly said that under the Victims' Rights Act it only has to notify victims when the leave is unescorted.
Independent victim advocate Graeme Moyle said public safety should outweigh offender rights regardless.
Moyle, whose brother Colin Moyle was the victim of insane killer Matthew Ahlquist in 2007, called privacy laws in such situations as "nothing more than state-sanctioned victimisation and another example of offender rights superseding those of the victim".
"At present the scales are weighted completely in favour of the offender. More weight needs to be applied to that of the victim," Moyle said.
He said Waitemata DHB and the Ministry of Health had a duty to keep the community safe from those whose illnesses made them a danger to others.
"This is a public safety matter and public safety should override privacy considerations on every occasion."
Moyle said victims of offenders in prison are informed of temporary release and this was no different.
Minister of Justice, Amy Adams, said there could be any number of reasons why a person might be granted escorted leave, including for something as routine as a dental check.