Few Edinburgh court cases in the past 100 years have generated such widespread public interest as the murder trial of trainee accountant William Laurie King.
Charged with the murder of his mother and attempted murder of his father, the 22-year-old's case gripped the nation throughout the summer of 1924 and made headlines as far afield as Australia.
King's alleged murder 'weapon' was not a blade or firearm, but a humble cheese sandwich - that happened to be laced with enough arsenic to kill his mother three times over.
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The accused lived with his parents and younger brother in a large detached Victorian villa in the capital's well-to-do Murrayfield district, and had been in training to follow in his father's footsteps.
Mr James Rae King was a successful and well-respected Edinburgh chartered accountant, who was dead set on his eldest boy pursuing an identical career path - but young Willie had other ideas.
Much to his father's bitter disappointment, Willie made it crystal clear he had little interest in accountancy. He saw himself as a scientist and was particularly fascinated by the field of chemistry, having set up his own makeshift laboratory in the house at Wester Coates Terrace.
On the night of May 30, 1924, the Kings sat down for supper, which consisted of buttered bread with cheese, jelly and coffee. It would be the last time they would eat together as a family of four.
Biting into his cheese sandwich, James Rae King began complaining of a burning sensation in his throat. His wife, Agnes, who was quite hungry, noted nothing wrong with her own sandwich and duly devoured it before finishing the half that her husband had left.
Within half an hour of the meal, James and Agnes started to feel quite ill and retired to their bedroom. It was not long before both parents started vomiting.
Mr King asked Willie to call the doctor, but he was out on another call. Instead, Willie managed to procure some brandy from the family's chemist, which helped Mr and Mrs King get to sleep.
At around 2am, James Rae King woke up and headed to the bathroom to vomit again. Upon his return to the bedroom he was met with a grim sight that stunned him to the core. Agnes was dead.
Acting on doctors' suspicions that the pair had been poisoned, the police were called in. Willie King's laboratory was raided and a cache of more than 150 bottles of chemicals taken away for testing.
What remained of the food the family had eaten that evening was also tested, but investigators declared no contamination of any description.
Agnes' post-mortem, however, was far more conclusive. The toxicology report found that her body contained a quantity of arsenic that was more than three times the fatal dose.
Days earlier, Willie had secretly obtained a large amount of arsenious oxide which he had illegally purchased from a contact at a motor garage.
Police investigators found a bottle containing the poisonous powder in his jacket pocket and discovered traces of the same substance around his trouser pocket.
On June 10, 1924, William Laurie King was arrested on suspicion of the murder and attempted murder of his mother and father.
Intense media interest surrounded William's matricide trial, which began at the High Court in Edinburgh on August 26, with the story making headline news across the English-speaking world. The scene outside the court at Parliament Square was one of pandemonium, with prying locals desperate to gain admission to the building.
Giving evidence before Lord Constable, a calm and collected William revealed he had a deep passion for chemistry and had been using arsenic in experiments. He stated firmly that he had not poisoned his parents.
Pleading not guilty, he told the court that a packet containing arsenic had been removed from his pockets by his mother and that this same packet had turned up on a shelf in the pantry the day after her death. He added that the packet had been slightly torn and that some of its toxic contents had spilled on the shelf.
William's father and brother backed up his version of events. They told the court that theirs had been a happy family and that William had no motive to poison his parents. They stated that they had not witnessed William sprinkle any arsenic on the supper they ate that evening.
On the third day of the trial, the jury gave their verdict, unanimously declaring the accused "not guilty on both charges". A deafening chorus of cheers and applause reverberated around the packed court room.
Guilty, not guilty, or not proven?
Author Jan Bondeson featured the story of William Laurie King's murder trial in his 2020 book Murder Houses of Edinburgh.
Summing up the case and questioning the King family's version of events, Mr Bondeson says the "not guilty" verdict was the wrong call.
The author wrote: "We know that Mrs King died from arsenic poisoning, and that a dose of at least 10 grains had been administered, a much greater amount than could be the result of accidental contamination. The case was definitely one of murder."
Jan Bondeson added: "Although I would agree that the evidence to convict William Laurie King was insufficient, I would myself tend to prefer a verdict of not proven in this particular case, one of the most baffling of the unknown and unsolved mysteries of Edinburgh."
