THIS is the blood-stained boot that meant Mark Weston could not get away with murder twice.

The 35-year-old odd-job man was yesterday convicted of killing Vikki Thompson in west Oxfordshire in 1995.

He had previously been acquitted of the mother-of-two’s murder after a 1996 trial, but a change in the law and new DNA evidence finally brought him to justice at Reading Crown Court.

Tiny splatters of Mrs Thompson’s blood on Weston’s footwear were missed by forensic scientists 15 years ago, but their recent discovery, along with newly admissible evidence of Weston’s semen on a pair of bras found at the scene, presented a compelling case to jurors.

Thirty-year-old Mrs Thompson had left the family home in Chestnut Drive, Ascott-under-Wychwood, on a warm August afternoon to walk the dog at about 4pm, having toasted the eighth anniversary of her marriage to husband Jonathan the night before.

More than three hours later she was found covered in blood and mortally injured beside a railway track off Shipton Lane.

Prosecutors believe Mark Weston, a life-long villager described by police as a “loner” with “no real friends of his own age”, had been performing a sex act at the scene and reacted violently to being discovered.

At the original trial at Oxford Crown Court in December 1996, the bras evidence was ruled inadmissible and, without the blood traces relied upon now, Weston’s lawyers twice argued unsuccessfully to have the case dropped due to lack of evidence.

Reviewing lawyer Denis Burke, who worked on the initial case, yesterday said: “The underwear in the plastic bags – the police and the Crown felt that was very important evidence.

“We felt we were able to say he was in the lane on that particular day. The matter was put before the trial judge and there was some legal argument for some considerable time. He was of the view that evidence was prejudicial. It was, to say the least, a major blow to the prosecution case.”

Describing what had changed in the analysis of the boots, Alison Levitt, the principal legal adviser to the Director of Public Prosecutions (DPP), said: “It’s not that techniques are different, but methods of examination have moved on.

“Looking for blood stains of this kind is really, really difficult. It’s a black boot with irregular surfaces and looking for blood stains involves a combination of the naked eye, a microscope where you can, and dabbing areas with a reactive agent.

“I think it’s accepted by everybody it’s almost as much an art as it is a science.”

The investigation into Mrs Thompson’s murder was re-opened in 2005 after a change in the Criminal Justice Act reformed the law on so-called “double jeopardy” cases by permitting retrials in very serious incidents in which new and compelling evidence had emerged.

Before this, no-one convicted or acquitted of an offence could be retried for the same crime.

Under the new legislation, prosecutors had to gain the DPP’s personal consent before applying to the Court of Appeal for an acquittal to be quashed and for a retrial to take place.

Mrs Levitt, said: “The threshold is an extremely high one for the prosecution to reach because although the legislation permits it, it’s accepted by everyone it’s an exceptional step to take.”

Describing how the new blood evidence was revealed, Pete Beirne, the head of Thames Valley Police’s Major Crime Review Team, said: “We got it in three phone calls.

“The first one said ‘we’ve found blood’. A week or two later, ‘it’s female blood’, and then a week or two after that, ‘it’s Vikki Thompson’s blood’ and it was euphoria.”

l There are currently 58 unsolved homicides dating back 50 years in the Thames Valley, 10 of which are being actively investigated.

tairs@oxfordmail.co.uk