IT was an horrific discovery that was to stun Britain. On a routine service on a quiet summer's day, a 12-year-old train spotter pushed open a toilet door - on the grubby floor lay the blood-soaked body of a teenage girl.

The boy ran screaming down the carriage and the Southampton-Reading diesel train, that had just eased out of Basingstoke station, screeched to a halt after a fellow passenger pulled the emergency cord.

Yvonne Laker the 15-year-old daughter of an RAF serviceman stationed in Singapore, was on her way back to boarding school on June 29, 1964, when she was dragged into the cubicle and had her throat slashed with a broken sherry bottle. She was identified by her grandparents, Major and Mrs Cyril Laker, of Barton on Sea, with whom she had been staying for the weekend.

Det Supt Walter Jones, Hampshire's senior detective, drafted in 50 officers to find the killer.

"She has been the victim of a frenzied attack," he told reporters. "It was a brutal attack and as far as I know a motiveless one. She has not been sexually assaulted."

Sixty passengers had been travelling on the train on the stopping service from Southamp-ton.

Yvonne had boarded the train at Southampton Central Station and her killer could have got on at any one of the seven intervening stations - Northam, St Denys, Swaythling, Eastleigh, Shawford, Winchester or Micheldever.

Yvonne was wearing a grey blazer over a blue-print dress.

Her blue holdall was found in the middle of the three-carriage train and her shoes and beret were recovered the following day, ten miles south of Basingstoke.

Detectives believed the killer may have accidentally left behind a major clue - a brown paper bag with a reinforced base similar to those supplied by wine merchants. Inside was a greaseproof paper wrapper labelled "Midland Dairy Maid Farmhouse bread" and four biscuits in a tin manufactured by Marks & Spencer.

Within hours about 40 passengers had contacted the murder investigation team at Basingstoke and been eliminated from the inquiry. Another 20 were unaccounted for, and detectives were anxious to trace one particular passenger who had been travelling alone in the front coach.

Despite appeals, the bag's owner failed to come forward, hardening the police belief it belonged to the killer.

However, the trail seemed to have gone cold until it was suddenly announced that a man was helping with police inquiries.

Nothing appeared to connect a father-of-three from the Basingstoke area with the killing. The 27-year-old had been arrested for motoring offences after his car crashed into a tree in north Hampshire.

He had persuaded a woman - unknown to him - to drive him to Farnham, Surrey, but on the way he got out and walked off. He was later arrested, charged and taken to Farnham police station.

But shortly before he was about to be taken into court, he made an extraordinary confession to PC Robert Eggerton.

"I'm worried," he admitted. "I was on the train the girl was murdered on, and I saw the man drag her to the toilet."

He was then asked to account for his movements on the day of the murder and the suspect recalled how he had gone to Basingstoke Labour Exchange and then to a pub in Church Street.

He then claimed he had boarded the wrong train at Basingstoke and instead of going to Winchester, where he planned to attend a Royal Marines recruitment office, he got on a Reading-bound service.

As he was charged with murder, he insisted: "I have had nothing at all to do with this, nothing whatsoever. I would never bring the shame on my wife and children."

His trial opened at the Hampshire Assizes in Winchester on November 23.

Jeremy Hutchinson QC, who led for the Crown, told the jury: "The prosecution does not suggest any motive for this crime. Of course, it does not mean the crime was motiveless. You may take the view that the people who do this kind of thing sometimes have reasons that we can all understand, and sometimes have reasons which are beyond the understanding of ordinary folk. It may be for some perverted reason - maybe due to imbalance, anger or rage."

He then outlined how the schoolgirl had been attacked as she sat on her seat, knocked unconscious with the sherry bottle that shattered on impact, and dragged to the lavatory, where her throat was cut.

He submitted: "It is a horrible and unpleasant murder because it was perpetrated in broad daylight on an ordinary summer's afternoon and on an ordinary train."

A railway porter told the court how he had seen the man get into the same compartment as Yvonne at Winchester and a police science officer said fragments of green glass found in his pocket were the same as others found at the scene.

The defendant never waivered in his defence that another passenger had slaughtered the schoolgirl, describing the killer as being about 30, 5ft 9in and wearing a sports jacket with a white shirt and a tie.

He maintained how he had seen a young girl and a man halfway down the carriage and then seen him steady her in the gangway with his arm around her shoulders.

"I asked him what was wrong and he said she is being sick," he said.

"The man reached for the door and I held it open for him, moving out of the gangway into the space between the seats. I sat down again and pushed the door shut. I didn't see them together again."

Minutes later, the man re-emerged and confirmed the girl was okay. "I asked if there was anything I could do and he said Mind your own business' or words to that effect."

The accused, however, could not account for the fragment of glass found in his pocket, other than suggesting it may be from a bottle that he had once taken home.

Signalman Fred Froude told the court how the train had slowed to walking speed just before the station and a series of witnesses confirmed they had seen a man acting suspiciously near the track before he ran off.

James Sharrocks, a look-out man for linesmen working on the track, was asked if the man he saw resembled the defendant. He replied: "That is not the person we saw."

After retiring for more than six hours, jurors filed back into court on December 1 to acquit him of murder. The defendant showed no emotion but his wife and his mother, who had flown in from America, threw their heads back in relief.

The verdict, however, did not bring freedom. The court heard he had been committed for trial on unrelated charges of arson.

He was alleged to have torched four barns in north Hampshire and set fire to furniture at a house in Basingstoke. He was later convicted in relation to one barn and the furniture, and jailed for 18 months.