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Qualtra, who had been a client of Joseph Marsden's.

Marsden's alibi for the night of the murder was that he was home in bed with the flu.

Gordon Parry claimed he spent the night with others, who could only loosely place him at their home between 7.30 and 8.30pm.

That night he also took his car to a garage for cleaning, where a witness reportedly saw a blood-stained glove inside the vehicle.

Regarding the night of the Qualtra phone call, Parry asserted that he had spent the day and evening with his girlfriend, Lily.

However, both Lily and her mother stated that he didn't arrive at her house until 7.35pm, partway through a piano lesson Lily was giving.

He then left on his own before returning much later.

The evidence against Gordon Parry and Joseph Marsden was largely suppressed by the police during the original investigation.

The spotlight on both men emerged decades after the crime, as armchair sleuths and authors took interest in the puzzling case.

One witness came forward claiming to have confronted Gordon Parry on his doorstep in 1966, 35 years after Julia's murder.

Parry allegedly displayed an astonishingly detailed knowledge of the crime and was aware of the deaths of several obscure witnesses connected to it.

He also boasted that he would never speak about it, even if offered a large sum of money.

Both Parry and Marsden died without ever admitting any involvement in the crimes.

The Wallace case, though seemingly straightforward, is often compared to a real-life Agatha Christie novel, a whodunit murder mystery featuring intricate puzzles, a closed circle of suspects, and detectives who solve crime using psychology rather than forensics.

The police's theory of how the crime occurred, portraying a suited gentleman turned sadistic killer wielding a blunt instrument and wearing a waterproof coat to avoid getting soaked in blood, evokes imagery reminiscent of Patrick Bateman, the protagonist of Brad Easton Ellis' controversial 1991 cult classic horror novel American Psycho, which some believe might have been inspired by the Wallace murder.

To this day, the case is still scrutinised in search of answers, with numerous new theories put forward, such as Julia harbouring a secret double life or the possibility that the Qualtra call was a red herring.

Perhaps it was simply a prank call and William did in fact murder Julia.

William then leveraged the existence of the call to his advantage, complicating what might otherwise have been a relatively straightforward case of domestic homicide.

On Saturday February 25 1933, just over two years after Julia Wallace was murdered, William Wallace died from the kidney disease that had troubled him for most of his life.

His last words spoken to his nephew before slipping into the coma from which he never awoke were, Do good with your life.