By Briony Leyland BBC Correspondent

A mystery which remained unsolved for more than 20 years was cracked thanks to advances in modern technology.

Schoolgirl Marion Crofts was just 14 when her life was cut tragically short at the hands of a murderer.

She had been cycling the five miles to school band practice from her home in Fleet, Hampshire when in Laffans Road, Aldershot, she was attacked as she passed dense undergrowth close to a canal.

Police later found her body in bushes close to the tow path. She had been raped, beaten and strangled.

Despite a major investigation during which officers considered 24,000 potential suspects Marion's killer was never found.

Samples

It was not until advances in forensic evidence gathering and testing were made, almost two decades on, that there was a major breakthrough.

DNA profiling was introduced in forensic work in the late 1980s and in the late 1990s technology had advanced enough for scientists to extract a full DNA profile of Marion's murderer.

To do this microscope slide samples taken from Marion's body and sealed in 1981 were opened.

It was a risk - if the tests did not work the samples could not be used again.

In July 1999 the DNA profile was entered into the national DNA database, but there were no matches.

One in a billion

Police re-opened the case - revisiting suspects and taking DNA swabs to see if a match could be found

Then in April 2001 police in Leicester arrested and charged a man for allegedly assaulting his wife.

Tony Jasinskyj - a 41-year-old lorry driver and former soldier - was routinely swabbed for DNA and the profile entered into the database.

It turned out to be a match for the profile of Marion's killer.

The chances of someone else sharing that profile are one in a billion.

Hampshire police discovered Jasinskyj had been a cook in the army in 1981, stationed in barracks in Aldershot - one and a half miles from the crime scene.

Lying

At the time of the murder he, like 1,500 other soldiers, had been asked to fill out a questionnaire about Marion's death.

On it he denies ever having been near the place where she was killed and claims he was at work at the time.

But Jasinskyj was lying.

When questioned about how his bodily fluids ended up at the crime scene, he said they had been planted there.

The jury agreed with the prosecution - there was no mistake - Jasinskyj was the person who raped and murdered Marion Crofts.

For Marion's family the four week trial has been harrowing but her father Trevor expressed his relief that her killer has been brought to justice.

Tony Jasinskyj's first wife who gave evidence at the trial said she had no idea he was responsible for Marion's murder.

The police have passed on their information about Jasinskyj to 30 other police forces - they say it is probable he is responsible for other serious crimes.