Bamber was convicted in 1986 of the murder of Ms Caffell, her twin sons and his adoptive parents. The court was told that Bamber shot his family and then placed the rifle in his sister's hands to make it appear that she shot them before turning the gun on herself.
The significance of the new material is now being considered by the Criminal Cases Review Commission, which Bamber's lawyers claim is close to referring the case back to the Court of Appeal. Bamber has lost previous appeals in 1987 and 2002.
Should the commission decide that the existence of the letter was overlooked at his original trial in 1986, and not explored at his two appeals, the disturbing case of Jeremy Bamber could once again face public examination. His legal adviser, Giovanni di Stefano, is convinced that the truth about the murders has still to emerge.
He claims the hand-written letter, which starts with the words "Love one another" is a lost suicide note. "This letter has not been properly considered in the evidence of the case and leaves us to conclude that there is either a conspiracy at work or those who have looked at the case are incompetent," Mr Di Stefano said. "What we need to ask is why this letter was never disclosed to the defence and if it is still in the possession of the prosecution, we need sight of it."
Bamber has always denied killing his adoptive parents, Neville and June, his sister and her twin six-year-old sons, Nicholas and Daniel, at the family's home, in Tolleshunt D'Arcy, Essex, in August 1985.
Bamber, 44, who stood to inherit almost £500,000 from his parents' estate, also believes other photographs not previously disclosed will prove he was in police custody when Ms Caffell died.
Solicitors said a medical expert had confirmed that the images show his sister covered in fresh blood at a time when he was already being held by officers. His legal team claims detectives initially suspected that Ms Caffell, known as "Bambi", failed to take her schizophrenia medication and murdered her parents and sons before shooting herself.
But in two appeals, Bamber has failed to convince the court that his conviction is unsafe, or the evidence used to convict him is unreliable.
Mr Di Stefano, the legal adviser who is now orchestrating Bamber's third appeal bid, is almost as controversial some of the clients he represents.
Born in southern Italy, he moved to Northamptonshire in 1961, aged six. He is said to have advised Kenneth Noye, convicted of murdering a man in a road-rage incident in Kent; Slobodan Milosevic, the Serbian President charged with genocide; Jonathan King, the pop impresario convicted of sexual offences against children, and Saddam Hussein.
Mr Di Stefano has a criminal record. On 18 March 1986, following a 78-day trial at the Old Bailey, Di Stefano (using the name "John") was convicted of fraud and sentenced to five years' jail. The amount of money involved in the fraud was reported at the time to have been £25m. In the same case, Di Stefano was also convicted of acquiring huge numbers of video tapes by deception.
Mr Di Stefano denies that his activities are being investigated and claims to be the victim of a campaign to blacken his name.
He told The Independent: "Despite people writing about police inquiries into my activities, which isn't true, I am still practising and am a member of the American Bar and the International Bar Association and qualified in Italy. I refuse to register with the Law Society so they don't like me. I deal with some very serious criminal cases and people seem to want to stop me doing my work. But I won't go away because if I don't help these people, who will?"
He claims he is still the lawyer of record for Saddam Hussein, against whom a civil action has been filed in a court of the District of Columbia. "This case against Saddam mirrors proceedings being brought in Iraq," he said. "I have asked the court in America for a stay of proceedings in this case. But if Saddam is found guilty, and I emphasise if, America, Britain and Italy have an agreement to put him in prison in one of these countries."
The legal battle
* 1986: Bamber, 25, is sentenced to five life sentences for shooting dead his adoptive parents, sister and twin six-year-old nephews at the family farmhouse in Tolleshunt D'Arcy, Essex, the previous year
* 1989: Court of Appeal throws out his first appeal
* 2001: Criminal Cases Review Commission refers Bamber's case to the Court of Appeal for asecond appeal
* 2002: He loses the second appeal
* 2005: Lawyers launch a third appeal against all his convictionsReuse content