Janet Brown was brutally murdered in her home near Chinnor on 10th April 1995.
The mother-of-three was savagely beaten to death in the quiet village of Radnage.
The 51-year-old was found naked, with her arms handcuffed behind her back and her mouth gagged with packing tape.
Nothing was taken from the detached house on Sprigs Holly Lane and there was no evidence Mrs Brown had been sexually assaulted.
The police say, confusingly, the killer tried to cut an entry hole out of a double-glazed patio door using a glass cutter, something the police say would have been difficult and time consuming, before smashing their way in.
Chief investigating officer Peter Beirne said "My working hypothesis at the moment is that it was a burglar, or burglars, who weren't particularly proficient.
"They came across Janet, they had control of her because they handcuffed her, and I think she was bludgeoned to death when she pressed the panic alarm."
Twenty years after the murder, in 2015, Thames Valley Police obtained a DNA sample believed to be that of the killer.
Since then they’ve swabbed more than 700 men, almost every male in the surrounding area, leading to no arrests.
Around ten months after the killing police received two anonymous answerphone messages from a male caller that seemed significant.
Investigators said at the time it was unlikely the calls were hoaxes and the tone and content suggested the caller believed the information was of importance.
Despite an appeal, the caller never came forward or tried to contact police again.
There is a £20,000 reward offered for information leading to an arrest and prosecution.