Mr Newman's Germany-based sister Sabine (who does not want her last name used) believes the police in New Zealand have not done enough to discover what happened to him.
English is not her first language but she told the Bay of Plenty Times Weekend by email: "The police have not done enough even (back) then. We are still very disappointed about the law enforcement investigations in New Zealand. In Germany this would be unthinkable."
She believed it was unlikely police would not do any more to find him.
"Today I expect nothing more.
"No police or investigation board is in contact with me or my brother and sister since three years."
Sabine visited New Zealand with her sister Brigitte shortly after Mr Newman's disappearance. She said her brother would never have abandoned his sons.
"Siggy has never neglected his children anytime. He was always there for the children. Someone who says, or thinks, that is not properly informed about the circumstances of Siggy and the children."
Police involved in the case did not return calls from the Bay of Plenty Times Weekend this week.
A search for Mr Newman by police and Land Search and Rescue volunteers began the morning after he was reported missing. It was abandoned after three days.
In 2008, police said a sighting by two parents placed Mr Newman at Pahoia School about 2.45pm on February 26, nearly a full day after the search began. However, police were unable to explain how he had travelled to the school at least 10km away when his car was still at Lund Rd, nor how he got there and disappeared again without being seen by anyone else.
Friends Andy Goodall and Peter Rae plan yet another search soon in the Kaimai Ranges, near where Mr Newman lived. Mr Goodall, who has experience in search and rescue work, carried out intensive searches for up to two months after Mr Newman went missing and distributed flyers throughout the district, asking people to check out buildings and other places on their farms where Mr Newman might have hidden.
"I've never really stopped looking. Every time I go into the area I look for any sign of him. I'd like to find Siggy for his family," said Mr Goodall.
In October 2009, police carried out another search but nothing was found. Two years to the day that Mr Newman went missing, the television physic investigation show Sensing Murder featured his story. A psychic suggested where he might be but the information did not result in his discovery.
Sabine said Mr Newman took his wife's last name when they married.
"He has decided to change his last name, because he loved Vicki very much. So he takes the name from his wife. He wants to build a new life with her in New Zealand."
Mrs Newman had been the family's breadwinner, while Mr Newman stayed home to look after the boys, although he did work at times in the kiwifruit industry.
Friends described Mrs Newman as a positive and strong woman who was the family's mainstay and kept her illness quiet for a long time.
LUANA WILLIAMS
Luana Deborah LaVerne Williams has been missing for almost 24 years. She was 26 years old when she disappeared from her Gate Pa home on June 5, 1986. Luana Williams was declared legally dead in February 1998. Her body has never been found.
JUDITH YORKE
Judith Anne Yorke has been missing for almost 18 years. It is believed she attended a party at Te Manaia orchard in Matapihi on October 21, 1992, and disappeared from there. She was 25. Judith's parents have refused to hold a memorial for her.
JOHN DUFF
John Duff disappeared on June 22, 2003. The 54-year-old failed to turn up for work after spending a night out in town. That evening, he went for a walk in Fergusson Park with his partner, who called their relationship off.
BOBBY ROBERTS
Te Paewhenua (Bobby) Roberts, from Te Puke, has been missing since November 30, 2004, when his van smashed through a barrier on the Kaimai Ranges and plunged 100m down the cliff. Mr Roberts, 53, was thrown out. Police are unsure if he is alive or dead.
