For 50 years, and through at least two moves to new addresses, 76-year-old Mrs McMahon had carried a terrible secret. Two of her babies had died shortly after birth and were not buried; instead, one was wrapped in a blanket in a tin trunk and the other was in a box, swaddled in a newspaper printed in 1945.
She had kept their existence a secret from everyone, even, according to her friends, from the husband she married several years after the births.
In the small village of Hoo, near Rochester, Kent, Mrs McMahon was known as a kind, upright woman, always meticulously dressed and ready to help her neighbours.
For 14 years, until 1980, she had visited the old and infirm around nearby Strood working as a home help, constantly prepared to lend a hand and - according to those who know her - ready with a willing smile.
In 1980, her husband, David, a former naval officer, bought a two- bedroomed council house in Knights Road, Hoo, and the couple prepared for retirement. He died 10 years ago. They had moved their possessions - as they had done earlier when Mr McMahon had postings in Portsmouth and Southsea - and Mrs McMahon took her babies with her.
She has carried them from home to home since they died during the Second World War. The pressures that resulted in her tragic behaviour are still being examined by police, but friends say she was a single young woman who grew up in a strictly religious farming family, thought to have been located near Heathfield, Sussex.
She lived there with her brother and sister who, together with her parents, were apparently unaware of the pregnancies. Police are trying to trace the brother and sister.
One officer involved in the case said yesterday: 'Her husband was in the Navy, but it is important to stress that they only met after all this. Mrs McMahon was never unfaithful to anyone.'
There are unconfirmed suggestions among neighbours that the father of the children may have been a soldier who died during the D-Day landings in June 1944 - a possibility that adds further to the tragedy.
'I nearly fainted when I was told what happened,' said Patricia Cruddas, one of her neighbours, yesterday.
'I have been a close friend for 10 years - but she never told me about the babies. She has a son but she often used to say that she would have liked a larger family. Perhaps that makes sense now.'
It was her son, Ian, 40, who discovered the corpses on Monday.
He had gone to her tidy semi- detatched house to do some chores following Mrs McMahon's admission to Medway hospital in Gillingham. She had fallen and broken her left leg and arm while tending the garden of a neighbour who had gone on holiday.
Mr McMahon, her only child, looked in the wardrobe and was, according to police, considerably shocked by what he found. Detectives and forensic scientists were then called.
A Home Office pathologist, Dr Michael Heath, conducted a post- mortem examination at Maidstone Hospital which showed that the babies had been born about 50 years ago but he failed to establish the sex of the corpses or the cause of death.
'This is a stable woman from a stable family and she is very bright, regardless of her age,' said one police source.
'She has co-operated fully and explained what happened. You have to bear in mind that she had the babies during the war and that she was not married. The social climate was very different for single mothers in those days.'
Two of her neighbours, Clifford Sturmer and his wife, Joyce, visited Mrs McMahon in Medway hospital on Wednesday and it appeared that her questioning by police may have been a release rather than an ordeal. 'I deliberately skirted round the issue because it is her business and not mine,' said Mr Sturmer. 'But she seemed fine. She seemed quite composed and calm in the hospital. I don't think she was worried about anything.'
He said Mrs McMahon has had a plate inserted into her arm and her leg had been set.
'We were as shocked as anyone when we heard what had happened, but Mrs McMahon has been a good friend to us over the years and it won't make any difference to our friendship.'
Dr Sheila Rossan, a lecturer in psychology at Brunel University in west London, agreed that the exposure of Mrs McMahon's secret may have positive results.
'I think this is a burden removed,' she said. 'A woman of her generation will be experiencing guilt and the way to purge guilt over a secret is to make it public.'
She said single women in Mrs McMahon's position in the 1940s were subjected to enormous social pressures. 'It would be worse for her, too, if she was from a religious family because she could not bear it if her children were not buried in hallowed ground.
'She will have been unable to mourn without being found out, and asking the vicar to perform a decent burial would lead to exposure. Perhaps that is why she kept them with her.'
Papers are now being prepared for the Crown Prosecution Service but it is by no means a formality that charges will be brought.
Prosecutors would have to consider whether the evidence she gave to detectives - suggesting either natural causes or foul play - could be corroborated. And, possibly more important, they would have to decide whether the public interest would be served by the prosecution of a 76-year-old woman who has suffered her own kind of imprisonment for half a century.