THE mother of a talented young scientist who was shot dead in his home 20 years ago has told how the unsolved murder of her only child has haunted her every day.

Pat Meenaghan, 82, of Stirling, spoke of the impact of the murder on her family as she made a fresh plea for help in finding Oxford University researcher Dr Michael Meenaghan's killer on the 20th anniversary of his killing.

Biochemist Mr Meenaghan was shot through a kitchen window at the back of his house in Monks Close, Blackbird Leys, Oxford, on December 10, 1994.

The 33-year-old, a lecturer at the Sir William Dunn School of Pathology, dialed 999 but died of massive chest injuries before police were able to reach him.

In the emergency call made just before 4.30pm, the operator heard someone struggling to breathe in the background.

Various motives have emerged for his killing, from links to Mr Meenaghan's private life and his work, to a case of mistaken identity.

The football fan known to friends as Spike was described as a friendly and pleasant man.

Despite an increased £20,000 reward being put up and an extensive investigation that included more than 800 people being interviewed within months of the killing, the murder remains unsolved, leading Mrs Meenaghan and cold case detectives from Thames Valley Police to renew their plea for information.

Mrs Meenaghan said: "It is now 20 years since Michael, my only child, was murdered.

"His death is always with me and there is not a day goes by when I don't miss him.

"We still don't know why someone would be so callous as to take his life and rob the world of a lovely man and a gifted scientist.

"Twenty years is a long time to wait for answers.

"There must be people out there that know something and could help ease the stress of not knowing why this happened to my boy.

"I would ask that people who do know something, search their conscience and make contact with the police."

Peter Beirne, from the force's major crime investigation review team, said: "Today on the anniversary of Michael's death, I am appealing to anyone who has any information about the offender, no matter how insignificant you think it may be, to come forward and speak to the police.

"Possible motives explored over the years have suggested links to Mr Meenaghan's private life, or to his work, or to a case of mistaken identity.

"However, there has been a lack of evidence leading to any conclusive motive and we have to keep an open mind as to what that is.

"If you know the identity of the offender or have any information that you think may assist please call us."

Julia Hughes, regional manager for Thames Valley Crimestoppers, said: "This is a horrific crime where a talented, young scientist was tragically killed.

"The motive for this attack still remains a mystery 20 years later and the culprit or culprits are still at large.

"They cannot go unpunished for this murder. They must be brought to justice.

"There must be someone out there who knows who is responsible for the death of Mr Meenaghan and we would urge you to contact Crimestoppers anonymously.

"We don't take personal details and you won't be expected to go to court or give a statement to police.

"We don't want to know who you are, just what you know."