A new law means murderers who refuse to reveal the location of the body could be denied parole.
Helen's Law is named after Helen McCourt who was abducted and killed in 1988 aged just 22.
Ian Simms, a pub landlord, was convicted of her murder but has never admitted to the crime or told police where the body is.
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The new law will come into play in England and Wales and follows years of campaigning from Helen's mother Marie McCourt.
In a heart-breaking interview with the BBC Marie said: "It's hard to lose a loved one in any circumstances, but to have them murdered is horrific.
"But then not to have their remains to be able to go and put flowers on, it's a grief that can't come out of you.
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"I could say I've had a dripping tap for on my head for the last 31 years. It's far worse than that, it's a pain in your heart that will never go.
"Families deserve to say a last goodbye and know where their loved one is going to be resting."
Almost 600,000 signed a petition Marie launched in 2015, calling for a change in the law which would mean convicted killers can't be eligible parole if they refuse to reveal where the victim's body is.
Speaking after the law was revealed, Marie said: "It has been a terrible stress on me since I started the petition in 2015. This law will help so many other families."
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Brave Marie also revealed that she had written to Simms 'begging him, please, please just tell me', but the callous killer didn't respond.
Helen was killed in February 1988 while on her way home to Billinge, Merseyside, from work.
Simms owned a pub near to her home and became a suspect in her disappearance early on.
He was convicted after blood and an earring that was the same as one belonging to Helen was found in the boot of his car.
He was given a life sentence and told he was would have to serve a minimum of 16 years before he could apply for parole.
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Justice Secretary David Gauke said in a statement: "It is a particular cruelty to deny grieving families the opportunity to lay their murdered loved one to rest, and I have immense sympathy with Marie McCourt and others in her situation.
"Helen's Law will mean that the Parole Board must consider this cruelty when reviewing an offender's suitability for release - which could see them facing longer behind bars.
"The profound grief inflicted on families and friends of the murdered is incalculable. Those responsible should know that if they choose to compound this further through their behaviour, they will be held accountable."
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