When spiteful, anonymous messages began dropping through the letter boxes of well-to-do Sheringham residents in the early 1920s, a series of events was set in motion that rocked the sleepy seaside town to the core and wove a web of intrigue worthy of an Agatha Christie mystery.

%image(14692572, type="article-full", alt="Dorothy Myrtle Thurburn outside Norwich Assizes with her mother Ada (left) and her solicitor, A T Chittock. Photo: ARCHANT")

And now, the little-known case of Sheringham's 'Unknown Hand' is set to be made public once more, thanks to the efforts of social history enthusiast Jane Crossen. KAREN BETHELL reports...

A former PA to Manchester rock legends the Stone Roses, Ms Crossen signed up as a volunteer at Sheringham Museum when she moved to the town from Cheshire five years ago.

Researching the seafront museum's recent First World War centenary exhibition, she discovered that the young owner of five wartime scrapbooks, Doris Hewitt, had been named as a witness for the prosecution in the 1924 trial of Dorothy Myrtle Thurburn, of Abbey Road.

%image(14692573, type="article-full", alt="Witnesses for the prosecution Mr and Mrs Christopherson outside court. The Sheringham couple received dozens of "scurrilous" letters.Photo: KAREN BETHELL")

A former Girl Guide leader, Miss Thurburn, 25, was accused of sending hundreds of 'poison pen' letters to the residents of Sheringham.

Written on notepaper and postcards, the letters, which began appearing shortly after the well-to-do young woman moved to the town in 1920, accused highly respected local people including stock brokers and solicitors and their wives of improprieties ranging from having extra-marital affairs and fathering children out of wedlock, to being 'badly made-up', 'walking like a duck', or having 'odd hips and twitching eyes'.

Miss Thurburn, who was arrested in November 1923 after a PC Brunson was set the task of following her and claimed to have seen her posting anonymous letters, was remanded on bail at Cromer. She appeared at Norwich Assizes two months later charged with 24 counts of sending defamatory letters to Sheringham residents.

The prosecutor accused Miss Thurburn, who pleaded not guilty to all charges, of sending libellous letters, including one accusing the wife of a local bank manager of being a 'low down cur' who was having an affair with her servant, and another sent to the wife of a solicitor saying she was a 'jealous, spiteful old cat' with 'dyed hair'.

%image(14692574, type="article-full", alt="Sheringham High Street in 1925, when the town was scandalised by the mysterious poison pen case.Photo: TIM GROVES ARCHIVE")

There was clear evidence, he said, that she had posted the letters, which were addressed to Sheringham residents who moved in the same social circles that she did.

A handwriting expert testified that there were similarities between Miss Thurburn's writing and that of the letter writer, with another witness saying that, after he confronted Miss Thurburn, the handwriting of the letters changed to 'printed characters'.

The defence pointed out that Miss Thurburn had also received anonymous letters and suggested that the jury could not possibly believe her guilty unless, rather than trying a young woman, the court was 'trying a young lunatic'.

The jury failed to reached a verdict and a second trial was scheduled, but the plot thickened further when Miss Thurburn's mother Ada wrote letters proclaiming her daughter's innocence to a number of newspapers and was forced to pay costs after being found guilty of contempt of court.

%image(14692575, type="article-full", alt="A page of a scrapbook put together by Jane Crossen, who has spent hours researching the case of Dorothy Myrtle Thurburn and the mystery of Sheringham's poison pen letters.Photo: KAREN BETHELL")

At Miss Thurburn's second trial, in Norwich in June 1924, Ada employed the famous barrister, Sir Edward Marshall Hall to represent her daugher.

Known as the 'Great Defender', Sir Edward had been briefed to represent the infamous serial killer Dr Crippen in 1910 and defended the 'Brides in the Bath' murderer George Joseph Smith in 1915. He was even said to have received a letter from Jack the Ripper saying that if he were ever caught, he would like Sir Edward to defend him.

Sir Edward made short shrift of the prosecution's arguments, forcing a surveyor called as a witness to admit that the policeman watching Miss Thurburn could not have seen her post letters from his hiding place outside the Morley Club, on Cromer Road, and the jury again failed to reach a verdict.

At the third trial, no evidence was offered by the prosecution and the jury returned a verdict of not guilty.

%image(14692576, type="article-full", alt="Jane Crossen, who plans to write a book after researching the case of Sheringham's 'Unknown Hand' poison pen mystery.Photo: KAREN BETHELL")

However, Sheringham folk were not convinced and, speaking to an Eastern Daily Press reporter after the trial, Miss Thurburn claimed to have received 300 anonymous letters, one of which suggested she take her own life.

'I never wish to see Norfolk again as long as I live, no-one knows what I have suffered,' she said.

It was later reported that Miss Thurburn and her mother planned to move abroad to escape the 'scurrilous' letters, which they had continued to receive months after her acquittal.

Ms Crossen, who has spent hundreds of hours looking into the case and gives 'Unknown Hand' talks to local groups, hopes to turn her research into a book. But, although sympathetic towards Miss Thurburn, she is not entirely convinced of her innocence.

%image(14692577, type="article-full", alt="Mr Justice Horridge, the judge in the first trial of Dorothy Myrtle Thurburn, who was accused of sending hundreds of poison pen letters to Sheringham residents.Photo: Archant")

'I think she may well have done it,' she said. 'She was certainly devious and it could be that she was just self-centred, needy and bored and wrote the letters for the adrenaline rush.'

Poison pen letters in history

* During the 1840s, a number of American printing companies began producing 'Vinegar Valentines', cheaply-made cards featuring unflattering caricatures and sarcastic, insulting poems. The cards remained popular until the 1940s, with printing companies all over Europe taking up the idea.

* In 1984, The Moving Finger, an Agatha Christie mystery featuring murder and poison pen letters, was filmed in Norfolk and Suffolk as part of the BBC Miss Marple series.

* In 2012, two Acle parish councillors quit after claiming they were victims of false allegations and had received a poison pen letter over a dispute at a village social club.

* In 2014, 50 people came forward after the EDP offered a £1,000 reward for information about the writer of more than 15 poison pen letters sent to elderly residents in Holt. A man eventually admitted sending the notes – some of which warned people to leave their homes – and was issued with a police warning.

* The Malicious Communications Act of 1988 made it an offence to 'send or deliver letters or other articles for the purpose of causing distress or anxiety'. The penalty for the offence is up to six years in prison.