Five years ago today, colleagues were stunned by the vicious murder of Oxford nurse Janet Brown in her home, writes Emma Henry.

The 51-year-old mother of three was found dead, naked and handcuffed, at the family home at Hall Farm, Radnage, near Thame, on April 11, 1995.

Despite an intensive police search, an emotional public appeal by her family days after the killing and a feature on BBC's Crimewatch UK, her killer has never been found.

Police have today issued a new appeal for information to coincide with the anniversary of her death and are still hopeful public support will help them solve this brutal crime.

Det Supt John Donlon, of Thames Valley Police, said: "Although thousands of lines of inquiry have been followed up during the past five years, we are still short of that one key piece of information which could help us to solve this crime.

"As in any murder investigation, this vital piece of information may only be a telephone call away, so on the fifth anniversary of Janet's death, we would ask people to search their memories as well as their souls and come forward with any information previously not given to the police which could help bring her killer to justice." Mrs Brown, a research nurse who worked for Oxford University's department of public health and primary care looking into the long-term health of women who had undergone fertility treatment, was bludgeoned to death at the foot of the stairs of her isolated farmhouse. She was hit around the head at least five times with a crowbar or jemmy.

She was at home alone at the family's 350,000 home when police believe she disturbed an intruder, who had broken in through the patio doors.

Her husband of 25 years, Dr Graham Brown, 50, a research scientist, was working in Switzerland and the couple's two eldest children Zara, 22, and 21-year-old Benedict, a student at Exeter University, had both left home. Their youngest daughter Roxanne, an A-level student at Wycombe High School, still lived at home but was staying with a friend on the night of the murder. The exact time of Mrs Brown's death is not known. A friend of Roxanne's rang the house at 8.30pm on April 10 and was the last person to speak to Mrs Brown alive. But her battered body was not discovered until the next morning by builder Nick Marshall and his son Ben, 15, who had come to do some work on the 11-acre estate.

Police say the motive for the murder has left them baffled. Although the house was broken into, the rooms were not ransacked and as far as the family can tell, nothing was stolen.

There was also no evidence of a sexual motive. Mrs Brown had not been sexually assaulted and, although she was found naked, her clothing was not discarded around her and her dressing gown was in her bedroom.

Unsuccessful appeals were made for a car driver and motorcyclist seen near Radnage around the time the murder is believed to have been committed.

Anyone with any information about Janet Brown's murder is asked to call Thames Valley Police on 01628 645678 or Crimestoppers on 0800 555 111. Police had several theories about why Janet Brown was killed, but have never been able to establish a definite motive.

THEORY 1: The Browns' house in Radnage had been on the market for several months and police believe her killer may have visited Hall Farm previously, posing as a buyer. Mrs Brown could have been killed because she recognised the intruder. But nothing was taken from the house on the night in question, making burglary an unlikely motive for the break-in.

THEORY 2: Detectives revealed after Mrs Brown's death that a prowler had frightened two other women in the area in the six weeks before her murder.

Det Supt Michael Short said at the time: "He didn't threaten them, as such, but they were put in fear."

The two women, one walking and one in a car, both walked off and only reported the incidents after the murder.

Police appeals to trace the prowler were unsuccessful.

THEORY 3: Detectives investigated at one point the theory that Mrs Brown's murder could be linked to the fatal shooting of Dr Michael Meenaghan at his home in Blackbird Leys, Oxford, in December 1994.

Both were working on medical research projects for Oxford University at the time of their deaths. But no definite link between the two unsolved murders could be made.

THEORY 4: Was the motive sexual? Mrs Brown was found naked, but there were no signs of sexual assault.

Her clothing was not scattered about her and her dressing gown was upstairs in her bedroom, implying she had come downstairs naked.

Story date: Tuesday 11 April

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