The man accused of murdering his lover and young son would have to be a “cold-hearted, callous psychopath” to have killed the pair, yet his lover told her best friend he had never been violent towards her, a court has heard.

Murray Macara KC, defending, told a jury that William MacDowell is innocent and did not murder Renee MacRae, 36, and their three-year-old son Andrew MacRae near Inverness on November 12 1976, and nor did he cover up the killings.

The High Court in Inverness has previously been told by Alex Prentice KC, prosecuting, that the now 80-year-old was the only man with the motive to kill because of the risk of his more than four-year affair with Mrs MacRae being exposed and him losing everything.

But on Wednesday, Mr Macara dismissed that theory.

“It’s a pretty dramatic solution to the potential problems that you’re going to kill your paramour and only son,” he told the court.

“If so, he must be a cold-hearted, callous psychopath – and yet Renee MacRae told Valerie Steventon (Mrs MacRae’s close confidant) he was never violent towards her.

“There was no benefit nor could there be if exposure of the relationship to Renee MacRae was a threat to his lifestyle, killing Renee MacRae and his son Andrew was a gross overreaction, so grotesque as to be absurd.”

He told the jury there “are no bodies” and there are “so many unanswered questions” in the case.

“The events of November 12, 1976 have been described as a mystery. It is still a mystery,” Mr Macara said, adding the defence did not concede they were murdered.

“If Mr MacDowell did have concern, love and affection for Andrew, how did he benefit from his death? How and why did he murder his only son?”

The jury was told that days after the mother and son disappeared, MacDowell had lost his job, lost his car and would possibly lose his home and children.

“There’s no proof he was involved in the disappearance,” Mr Macara said. “It’s speculation, it’s always been speculation.”

Mr Macara said a number of witnesses had been called to give evidence, and they were being asked to recall evidence from more than four decades ago, including one witness who recalled she heard a “blood curdling scream”.

Mr Macara said: “How reliable are our memories from four or five years ago, let alone 45 years ago? Distant memories can distort the truth.”

He said police officers were told the “blood curdling scream” was a “distinct screech”.

Mr Macara said many witnesses have since died or are no longer capable of giving evidence in person, and the trial has had to rely on statements, including a statement read out by Mrs Steventon.

“In this evidence we have what William MacDowell says to Renee MacRae, what Renee MacRae says to Valerie Steventon, and what Valerie Steventon says to the police,” he said.

“It’s Chinese whispers and we know Chinese whispers quite often distort what the original message is.”

The court has previously heard of blood discovered in the boot of Mrs MacRae’s burnt-out car.

But, holding a teaspoon, Mr Macara told the court the amount of blood was a “very, very limited amount of liquid”.

He said: “One-and-a-half teaspoons. Less than you take from a cough bottle.”

MacDowell, of Penrith in Cumbria, is on trial charged with assaulting Mrs MacRae and Andrew at the Dalmagarry layby on the A9 trunk road south of Inverness, or elsewhere, by means unknown, and as a result murdering them.

He is also accused of disposing of the bodies of Mrs MacRae and her son and also disposing of a boot hatch from his Volvo car to defeat the ends of justice.

MacDowell denies all charges against him.

On the Volvo, Mr Macara said his client was under pressure to return the car after he had been sacked by his boss – Mrs MacRae’s estranged husband Gordon MacRae – and he asked the jury to accept his explanation that the hatch had broken.

MacDowell has lodged a special defence of incrimination and alibi, part of which is that he was at the Mercury Motor Inn, Inverness, that evening before going home via his work and a shop, and that Mr MacRae was responsible for the killings, if they did happen.

Mr Macara posed the question to the jury of Mr MacRae’s motive, in that despite he too having an affair, the relationship between MacDowell and Mrs MacRae might have affected his standing and might have been a “visible source of embarrassment”.

But he admitted the incrimination evidence was “extremely limited”.

There has also been evidence of sightings of a man with a “Mexican moustache” in the company of Mrs MacRae. Mr Macara told the court there were 123 potential sightings of Mrs MacRae after November 12, but not all were eliminated.

“It only takes one and the Crown case is bust,” he said.

On Tuesday, the defence did not call MacDowell into the witness box to give evidence.

Lord Armstrong, as he began to give instructions to the jury, told them they should draw no adverse inference from this and his innocence is presumed.

The trial continues.