DNA evidence left at the scene of a violent murder two decades ago could finally help investigators track down the person who brutally beat to death a mother-of-three, it has emerged.

Her daughters have urged anyone who knows anything about the "horrendous" killing of their "kind and loving" mother to speak out, as police launch a swabbing programme they hope will lead to the murderer being unmasked.

Primary care nurse Janet Brown, aged 51, was gagged using packing tape, handcuffed and beaten around the head at her home by something similar to a crowbar on April 10, 1995 - 20 years ago to the day.

Her naked body was found at the foot of the stairs of the family home in Radgage, Buckinghamshire, by builders who had arrived to carry out work.Her killer has never been found - but, on the anniversary of her death, detectives have revealed a possible breakthrough thanks to modern scientific techniques.

Janet Brown was gagged, tied up and beaten at her Buckinghamshire home Credit: PA

Peter Beirne, the head of Thames Valley Police's major crime investigation review team, said a DNA sample belonging to an unknown person had now been successfully extracted, though he would not say from what item the sample had been taken.

Police now plan to swap a number of people who featured in the original investigation, and Mr Beirne urged anyone who suspects someone of being involved to tell police so they too can be tested.

Janet's death left three children without a mother. We want to bring justice to Janet's family.

Peter Beirne, Thames Valley Police

If nothing comes from the appeal, he added, there could be a "potential mass screening" in the area.

Mrs Brown's daughters, Roxanne and Zara, shortly after the murder Credit: PA

The motive behind the killing - described by detectives as "heinous" and "horrendous" - remains unclear.

The handcuffs and tape used on Mrs Brown had been brought in by the killer, and while a window was broken and the burglar alarm triggered, suggesting a break-in gone wrong, nothing was taken from the home. There was also no evidence Mrs Brown had been sexually assaulted.

Her daughters Roxanne and Zara, who were aged 18 and 23 at the time, were out on the night of the murder, as was their brother Benedict, then 21.

They said the horror of their mothers death "stays with us every day" - and said they believe it was pre-planned.

She was attacked and killed in our family home - a place where we should all be safe.

Roxanne and Zara Brown

A £20,000 reward is being offered to anyone who can provide information which leads to the conviction of the killer.