Ashburton teenager Kirsty Bentley was 15 when she went missing in 1998.

Every time a child goes missing, a small number of families draw a deep breath. They have been through it all before. TOMMY LIVINGSTON talks to some who know how hard it is to sit and wait for that knock on the door.

Shortly after it was announced Alex Fisher's body had been found, cars began gathering outside his home in Levin. Inside, a family were coming to terms Alex was no longer missing, he was dead.

Doug Blakie watched the news with sadness, only too familiar with the agony facing the Fisher family.

In 1999, his daughter Lisa, 20, went missing while hitchhiking along Arthur's Pass in the South Island.

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For four days, he had no idea where she was, until he heard the news he hoped he would never receive.

"A report came across the news on national radio that a body had been found. Straight away, I knew it was Lisa," he said on Friday.

"The nightmare continues from then on."

Lisa Blakie went missing in 1999.

Lisa had been brutally murdered and left in a stream. A massive police investigation ensued to catch her killer. After an arrest was made, Blakie had to endure the court case.

One of the hardest parts of watching the police investigation unfold was waiting for bad news, he said.

"It is very hard for the family to sit and wait to hear that knock on the door. It's a hell of an experience. It's one you don't wish on anyone. Our hearts go out to the [Fisher] family. You feel teary-eyed thinking how the hell did this happen."

Judith Furlong can also relate. Her daughter, Jane, 17, was abducted in 1993. She remained missing until 2012, when her remains were found in the sand dunes of Sunset Beach in Port Waikato. Her killer has never been caught.

Furlong said the initial reaction when your child went missing was gut-wrenching.

"It's disbelief that this is happening. You start asking why is it happening to you. It is hard to take it in, in the beginning. You naturally go onto auto-pilot. I can remember it like it was yesterday."

Jane Furlong was abducted in 1993.

Constant attention by police, media and the public was surreal.

"It is total trauma. Your house becomes like grand central station. Every five minutes, there is another policeman there. That's very freaky. One minute, you are an ordinary person going about your business, the next thing. it feels like the whole world has got a spotlight on you."

Another challenge was having your child's face splashed around on the news, she said.

"It's a shock to suddenly become known, and you don't want to be known. But it's a two-edged sword because you have got to go to the media because you need their help."

Media attention is something John Bentley knows a lot about.

His sister, Kirsty, 15, went missing while walking her dog along the Ashburton riverbank on New Year's Eve in 1998.

Two weeks later, her decomposed body was found in a secluded gorge. Like Jane Furlong, her killer has never been caught.

Bentley said it took a while for him to realise there was anything sinister about Kirsty's disappearance. Ashburton, like Levin, was a quiet town and he was sure his sister would return home.

"The idea of something significant happening was so silly. I expected the reason we did not know where she was to be something simple, like she had gone to a friend's place and not told anyone," he said.

"I realised that the situation was serious much later. By then, I was just numb as I really didn't have any experience with this sort of thing."

Bentley, along with his father, were considered suspects in Kirsty's disappearance.

Initially, he thought the police attention was natural, but once he realised they suspected he was the killer, that illusion slipped away.

"When they first interview you, you know it's procedure and don't have any doubts. Once they decided there was a possibility that one of us could have done it, I began to doubt reality.

"I know I didn't do it and so I expected that telling the truth would prove my innocence. When it didn't, it messed with my head a bit."