A BBC documentary is set to claim that a mystery man could have been living in the house where Lord Lucan's nanny was killed.
It is thought the man could have been a boyfriend of one of the women living in the property where Sandra Rivett was bludgeoned to death in 1974.
The BBC documentary has uncovered evidence that Lord Lucan's daughters said a "boyfriend" was staying at their home at the time Rivett was murdered.
The BBC was handed notebooks and tapes by the daughter of the late David Gerring, a detective chief inspector who worked on the case.
Lady Sarah Gibbs appears to have told police at the time that the Lucans' young daughters talked about a "boyfriend" at the home, the BBC Inside Out programme has learned.
The murder of Sandra Rivett in 1974 sparked the biggest manhunt in Scotland Yard's history, and the 7th Earl of Lucan vanished after the death. An inquest found that he murdered her.
Lord Lucan had later claimed in a letter that he had seen a man fighting with his estranged wife in the family home, but that the man had fled.
In the documentary, which airs tonight, it is claimed that Lucan’s late sister-in-law, Lady Sarah Gibbs, had a conversation with the peer’s daughter Camilla, then four.
During the conversation the child is said to have suggested there was a man living in the London home along with her sister Frances, brother George and mother Veronica.
It is claimed that Lady Sarah said her four-year-old niece, Lady Camilla Bingham, spoke of a mystery man who sometimes slept in "nanny's room and nanny sleeps with us".
Asked whether the man was the nanny's boyfriend or Lady Lucan's, Lady Sarah, who died in 2001, responded: "I wouldn't know, I'm assuming she meant the nanny because Frances [her 10-year-old sister] referred to the boyfriend when I told her that the nanny was dead."
Lord Lucan's brother, Hugh Bingham, has called for the evidence to be looked at afresh, and told the BBC he was annoyed that the statement had not be presented at the inquest in 1975.
The documents obtained by the BBC also reveal that police believe Lucan could have been in Mozambique up to 2002. They also show police believe Lucan visited a Scottish estate in the late 1970s.
Lord Lucan has been missing since the day after Sandra Rivett was found battered to death. His car was found abandoned in Newhaven, East Sussex.
He was officially declared dead by the High Court in 1999.