If the murders were shocking, the court case was sensational.
TV stations and newspapers descended on the city. The prison service had to send out a decoy van to prevent angry mobs attacking Manuel as he arrived.
Manuel was one of the first defendants in a Scottish court to represent himself.
He failed to convince the jury who convicted him on seven counts of murder.
Seventy years on, Denise Mina believes there are still further details to uncover about the crimes.
“After The Long Drop two of the sons of one of the victims came to see me.
“They said they were sure that William Watt was not an innocent who happened to meet his family’s murderer, that he had commissioned somebody to kill his wife.
“They said they had been trying to tell people the real story for decades but no one would listen, because as soon as the case was over everyone decided that was the end of it.”
“And they told me amazing details like he had gone fly fishing up at the Crinan Canal and he took the guard dog with him – a three-year-old golden Labrador – which is the last thing you want when you are fly fishing.”
“I was mad that I didn’t get that detail in.”
“But mostly now it’s people saying, I remember when that happened when I was a kid.
“And people’s mothers would threaten them, ‘If you don’t go to bed now, Peter Manual will come and get you’.
“Which is a very Glaswegian style of parenting.”
