Arlene Fraser's family has said her killer husband should remain in prison until he tells them what happened to her.

Her disappearance in 1998 sparked one of the biggest ever police investigations in Scotland and resulted in a murder conviction for her estranged husband.

Nat Fraser was sentenced to at least 17 years behind bars after a retrial in 2012, despite Arlene's body never being found.

Speaking to STV News ahead of the 20th anniversary of her death, her relatives admitted that they have given up hope that Fraser will reveal how she died, but say he should only be considered for parole if he finally tells the truth about what happened to Arlene.

Arlene's brother-in-law Steve Gillies said: "She shouldn't be forgotten.

"I don't think people, certainly in the north of Scotland have forgotten about her and I wouldn't want them to. Arlene is the focus of this and it's right and proper that she should be remembered.

"Arlene was a bit of a firecracker and she liked a good time. She was really different and quite a vibrant character."

Despite Nat's refusal to reveal any details Arlene's family is still hoping that someone out there will know the truth.

Steve said: "I just have a feeling that there will be something that'll happen, not tomorrow or next week but I think there are people out there who know a bit more about this than they've told and their conscience might be pricked by something to actually come forward to let us know what happened."

Arlene was last seen in April 1998 as she waved her children off to school.

Her disappearance sparked a major investigation and an appeal from her husband to come home.

But in 2003, five years after she was last seen, Nat Fraser was convicted of hiring a hitman to kill her after he learned that she was planning to divorce him.

One of the detectives at the head of the investigation into Arlene's disappearance said Nat was a "dark and cunning" killer who thought he had committed the "perfect murder".

Alan Smith, a former detective superintendent at the old Grampian Police, said: "I think the real Nat Fraser is a very dark and cunning individual who had the confidence to sit down and mastermind what he thought was the perfect murder to get his wife, for his own selfish reasons, out of the equation so that his life would be seemingly easier.

"Nat is an individual who absolutely needed control of his life and those around them and he's gradually lost that control.

"He's lost his freedom and his family, he's lost his business and so in prison the last piece of control that Nat Fraser has is that secret that he'll probably take to his grave."

In the years following his conviction Nat repeatedly appealed and claimed that the "fight isn't over".

He eventually had his conviction quashed by the Supreme Court but was again found guilty at his retrial in 2012.

But Arlene's family said he shouldn't be considered for parole until he reveals details about her murder.

Steve said: "The family are in a bit of limbo because of all of this but at this stage I can't see that happening to be honest with you.

"There's nothing that's happened in the last few years to indicate that Nat will ever admit anything about this."

In a statement, the family said: "Sadly, the 20th anniversary will feel the same as any other anniversary. It is a day we dread, and we cannot hide from the frustrations, memories and emotions that are stirred at this time each year.

"We have reached a cross roads where we must consider whether finding Arlene's remains would be good for us or not.

"The brutal truth may be too hard to bear, however it would put an end to the waiting.

"In the meantime, we would like to take this opportunity to thank everyone for their continued support .

"Public and media interest in Arlene has never faded and for that Arlene's parents and sister will always be grateful.

"Fraser was given minimum of 17 years in May 2012, he has 11 years left to serve before he can ask for parole.

"We feel that a condition of his parole should be that he provides more information on what happened to Arlene."