Furthermore, he'd talked to Julie before the killings about wanting to get rid of them all, speculating about the perfect murder.
On the night of the massacre, she said, Bamber rang to say: "It's tonight or never."
He added that he'd hired a hitman, called Matthew McDonald, for £2,000. She could prove he was dishonest because they'd burgled the family-owned caravan site together five months earlier.
At the eventual murder trial, Julie's evidence was vital to the prosecution case. The Crown argued that Bamber detested his parents for having sent him to boarding school, and resented Sheila's success and the allowances they made for her state of mind.
But his chief motive, said the prosecutor, was to inherit about £435,000 and 300 acres of land.
The rest of the case seemed cut and dried. Sheila would not have known how to use the gun, which would have had to be reloaded at least twice.
The silencer would have made the gun too long for her to point at herself, and she couldn't have returned it to the cupboard. There were no bloodstains on her body or her nightdress and no traces of firearms residue - except a bit of lead on her hands.
There was no documentary evidence - as there would be today - to back up Bamber's claims of the phone call he received from his father.
On October 18, 1986, ten of the 12 jurors returned a guilty verdict.
Sentencing Bamber to life, Mr Justice Drake described him as "warped, callous and evil".
With hindsight, the case against Bamber was thin. There was no evidence that he had travelled from his home to the farmhouse and back again in the early hours of the morning.
Nor was there forensic evidence linking him to the crimes, other than one of his fingerprints being on the gun. But he admitted using it previously to shoot rabbits and Sheila's fingerprint was also on it; as were those of the policeman who'd picked up the gun after the murders.
When the silencer was found, no one who handled it had worn gloves to try to retain the evidence.
However, there was a flake of blood inside, and the forensic expert who analysed it concluded that it came from Sheila - backspatter (a spray of blood from the victim) after she had been shot.
However, another expert, who also gave evidence for the Crown, said that the .22 Anschutz was unlikely to produce backspatter - and even less likely to when fitted with a silencer.
Major Freddy Mead, a firearms expert appearing for the defence, noted that there were no grounds for believing that the silencer had been used at all during the attacks.
No one could even be sure that the blood in the silencer was Sheila's. The blood tests available at that time were basic. All that could be done was blood grouping.
The prosecution later conceded that Sheila's blood group matched that of Robert Boutflour, Jeremy's uncle, who was present when the silencer was found.
Other scientists said that the flake could have been a mixture of Nevill's and June's blood. The jury had asked whether this was a possibility.
There was also blood on the barrel of the rifle; again, no one knows whose.
It would be invaluable to learn more about this evidence, using scientific techniques available today.
But this is impossible because Essex police destroyed many of the original trial exhibits, including all the blood-based samples, in February 1996.
Those responsible insisted they had not realised that the exhibits might be needed - yet ever since the conviction, this case had been a hot topic.
In February 1996, it was still under consideration by the Home Office and was one of the first to be transferred to the new Criminal Cases Review Commission, which said the destruction of scientific exhibits was "in breach of the force's own guidelines".
Bamber's lawyers have always believed that Nevill and June were shot in their bedroom. June struggled across it before collapsing, while Nevill, having been shot twice, managed to get downstairs to reach the telephone and call Jeremy.
He then struggled with his assailant, who beat him with the rifle butt before shooting him dead. The prosecution maintained that there were signs of a tussle, with furniture being overturned, which meant that Jeremy, not Sheila, must have been the attacker.
However, according to a document later released by City of London Police (which had been asked in 1991 by the Home Office to conduct an independent inquiry into Essex police's handling of the investigation), the officers knocked over chairs when they burst into the house.
Further, Sheila could have subdued Nevill; having been shot twice, he would have been weak.
Also, it was possible for Sheila to have shot herself twice. The first wound, to her throat, was fired from a distance of three inches but would not have killed her instantly; the second, fired with the barrel pressed against the skin, would have done.
But could Bamber have shot her?
There was no evidence that Sheila had resisted and Bamber would have needed to be underneath her, with her acquiescing, in order to fire the shots at the angle they entered the body.
In effect, he was convicted on the evidence of his own conduct after the shootings, as well as the word of one scientist and his former girlfriend.
Yet not only did her account contradict much of what she had originally stated; it was not supported in crucial ways. The alleged hitman, Matthew McDonald, who gave evidence at the trial, had a strong alibi.
The Criminal Cases Review Commission referred the case to appeal in March 2001. The appeal began in October the following year.
By then, as much scientific testing as possible had been carried out.
The appeal court judges determined that June Bamber's DNA - but not necessarily Sheila's - was in the silencer. They added, however, that they believed there had been significant contamination of the samples and the results were meaningless.
Looking at the case as a whole, they concluded in December 2002 that "the deeper we have delved into the available evidence, the more likely it has seemed to us that the jury were right".
Bamber responded to the disappointment by changing his legal team.
Bamber's defence depends on whether Sheila was a viable suspect. Her family did not think she was capable of serious violence.
"Apart from the odd occasion when she has struck me in a temper," said her former husband, Colin Caffell, "she has, to my knowledge, never struck anyone."
However, Dr Hugh Ferguson, consultant psychiatrist at St Andrew's hospital in Northampton where she was treated, reported that she was "caught up with the idea that the Devil had taken her over and given her the power to project evil on to others, including her sons".
When she was discharged from hospital in September 1983, Ferguson wrote that she had thoughts that she was "capable of murdering her own children".
He made a "firm diagnosis" of schizophrenia, prescribing the antipsychotic drug Stelazine.
She was re-admitted in March 1985 and received injections of another anti-psychotic drug, Haloperidol.
The drug was found in her bloodstream when she died (as was cannabis).
As the appeal court judges said, "She had a psychotic illness requiring in-patient treatment. She had severe mood disturbances (schizophrenia) and she used cannabis and cocaine."
Learning of the killings, Dr Ferguson initially said that such violence was incongruous with his view of Sheila.
Yet, when told that it had been suggested that her children be taken into foster care, he said that this could have had "a catastrophic effect".
He added: "I would not have expected her to be passive about that."
Dr Ferguson said in his evidence that it would have transformed her image of her father from "a support and mentor into a hostile figure".
Instances of psychiatric patients murdering others and then themselves were almost unknown in 1985-6. But they have occurred with tragic regularity in the years since, particularly in the United States.
Bamber's current lawyer is the controversial Giovanni di Stefano. Born in Italy, di Stefano was raised in Northamptonshire and has built a practice in Italy and Britain. His clients have included Saddam Hussein and Slobodan Milosevic.
Di Stefano has found the previously lost statement of the first officer to enter the house, at 7.34am.
The officer stated: "(Sheila Caffell) had what appeared to be two bullet holes under her chin and blood leaking from both sides of her mouth down her cheeks."
This puts the case into a fresh light. If blood was still leaking from Sheila's wounds, then she had died relatively recently, and certainly long after the time that Bamber called the police.
It also fits with other evidence. That night, as police waited with Bamber at a safe distance from White House Farm, they said they saw someone moving through the house. That has always been known. Later, it was assumed they were mistaken. Perhaps they were right all along.
It could explain too why Sheila was not bloodied and had only traces of lead on her hands. She could have washed herself and changed before killing herself.
Professor Bernard Knight, a pathologist who gave evidence at the trial, said that those committing suicide would often engage beforehand in "ritualistic" cleaning.
One final aspect of the case that has never been given attention is - assuming Bamber was guilty - why would he have invented such a preposterous story about the phone call from his father?
It would have been simpler for him to go back to bed, make himself scarce and let it appear that there had been intruders.
The idea that he could invent a tale of a killing spree by a mentally disturbed woman to be lent credibility by further violent episodes over the following decade is hard to credit.
Following the lie-detector test, the case is now set more favourably for him than it has ever been.
Maybe the truth will still come out in the wash.
Article courtesy
DailyMail.co.uk