However, convicted killer Jeremy Bamber has reportedly claimed he has "the ultimate alibi" that proves his innocence.
According to The Sun, 58-year-old Bamber has indicated from his cell in West Yorkshire that he has evidence that members of his family were still alive in the house AFTER police say they had been slain.
Bamber is currently serving a life sentence in HMP Wakefield after being found guilty of murdering parents June and Nevill Bamber, as well as sister Sheila and her twin boys Nicholas and Daniel, in a remote Essex farmhouse in August 1985.
However his lawyer insists that "strong" new evidence has come to light which makes Bamber's conviction uncertain.
Bamber is reported to have said: "It is the ultimate alibi that I was in the company of dozens of police officers when it was clear that a person or persons were alive in the house who I am convicted of murdering."
These things shouldn't have been happening at those times if it was Jeremy.
Police asserted everyone in the house was already dead by 3.30am on the day of the murders - but defence lawyers claim a rifle was spotted in an upstairs bedroom window at around 7am later that morning.
They have also put forward that police did not enter the house until four hours after receiving a telephone call from inside over fears someone inside might be alive - and armed.
The purported evidence - shared by The Mirror's website - is said to show a BT operator connected police to an open line at the farm at 5.50am.
According to the tabloid, this document suggests the handset might have been replaced back onto the phone to ensure a claimed call to 999 at 6.09am could be made.
Bamber's legal team continues to insist he was not behind the grisly deaths and that Sheila was still alive as police first entered the property.
They also point to evidence that suggests windows may have been opened after 3.30am and lights turned off between 4am and 5am.
"Because I haven't received evidence that contradicts it, I can't necessarily say it isn't anything other than it was Sheila," Bamber's lawyer is reported to have said.
"These things shouldn't have been happening at those times if it was Jeremy. So it causes a real worry."
Police initially believed that Sheila - suffering from mental health problems at the time and on medication - carried out murder-suicide.
But attentions soon turned to Bamber after he began to behave erratically - and his girlfriend later told them he was responsible for the atrocity.
White House Farm concludes on ITV tonight at 9pm
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