This information could have prevented Manuel's execution because it would have allowed the High Court to accept a plea of diminished responsibility.
Dr Goldberg has studied files held in the National Archives in Edinburgh which have been released following a request from BBC Scotland, made under the Freedom of Information Act.
He said the files proved the legal and political authorities in 1958 knew Manuel was a psychopath, but sought to minimise that fact because of the widespread public outrage caused by his crimes.
He said: "Some very important documents were made available as a result of the Freedom of Information request by BBC Scotland.
"I am now more convinced than ever that the authorities played down Manuel's psychopathic personality in the days ahead of his execution, because they had come to the conclusion that he should not receive a reprieve."
Dr Goldberg believes the case highlights the need for a re-examination of the way in which the Scottish criminal justice system still deals with psychopaths, more than 50 years after Manuel's execution.
"It still matters today because Scots law continues to have problems with people with psychopathic personality disorder," he said.
"If somebody is a psychopath, then the law states that cannot form the basis of a plea of diminished responsibility.
"There has been a reluctance to understand the nature of psychopathic personalities since the 1940s."
BBC Scotland has also obtained a recorded interview with Peter Manuel, made by a psychiatrist while he was being held at Barlinnie prison.
The interview can be heard in "Peter Manuel: Inside the Mind of a Psychopath", on BBC Radio Scotland.
It is the first time the voice of Scotland's most notorious murderer has been broadcast.
In the recording, Manuel can be heard discussing the murder of the Smart family, who were shot dead in their bungalow in Uddingston on New Year's Day 1958.
Manuel is described as sounding remarkably composed. He denies the case against him is "authentic" and the psychiatrist's suggestion that the situation he has found himself in is "very grave".
In another development, the programme makers have obtained the notebooks Manuel used to plan his defence. These include a sketch showing where Manuel buried one of his victims.
The body of the Lanarkshire teenager, Isabelle Cooke, was only discovered after Manuel led detectives to the ploughed field where he had buried her.
BBC Radio Scotland's Investigation programme, "Peter Manuel: Inside the Mind of a Psychopath" was broadcast on Monday 16 February.
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