She had suffered from mental health problems in the past and seen a psychiatrist after becoming depressed.
Mr Venables lied to police about the affair and later downplayed its significance, insisting his wife had been depressed because she had been unable to have children.
But Mr Burrows went on: “The truth, say the prosecution, is that it was David Venables who killed her. He wanted her out of the way: he wanted to resume his long-standing affair with another woman.
“He knew about the septic tank in its secluded location. It was for him almost the perfect hiding place.”
He added: “And for nearly 40 years, it was the perfect place and he got away with murder.”
The jury heard that when he went to the police to report his wife’s disappearance, one of the officers noted that he “did not seem anxious in any way and was quite calm”.
Another officer described him as “cold and showed no emotion and did not seem worried in any way”.
Ms Styles had also described her lover as remaining “quite composed” and “calm” after his wife went missing.
The police concluded there was no evidence that he had murdered his wife and it remained as a missing person’s enquiry.
By 2019 Mr Venables had sold the farm to his nephew, and it was in July that year that contractors, clearing out the septic tank, found bones, including a human skull.
In July 2019, when police contacted him to confirm they had discovered his wife’s remains, he expressed surprise, pointing out that the septic tank had been cleaned out several times before.
Mr Burrows told the jury: “He also said that around the same time he knew another woman who had gone missing.
“He said she had been picked up by Fred West and managed to get out of his car.”
On July 30 2019 a police officer again went to his home and arrested him. That day and the next day, they searched his property. In the dining room there was a book on Fred and Rose West
Mr Venables sat in court wearing a suit and tie and earphones in order to follow proceedings.
The pensioner denies murdering his wife between May 2 and May 5, 1982, and the trial, which is expected to last up to last six weeks, continues.