A former Scotland Yard detective claims to have discovered what happened to Lord Lucan.
Other detectives are not convinced
Duncan MacLaughlin says the peer died in the Indian state of Goa in 1996, where he had been living under the name of Barry Halpin.
Ex-detective, Mr MacLaughlin, says in the book - Dead Lucky - that photographs of an elderly man taken in 1991 and passed to him resemble the missing Earl.
Mark Winch, who took the pictures, said he befriended Halpin whilst in Goa.
In the book, Mr Winch says he was a well-spoken gambler who played backgammon, a
pastime for which Lord Lucan was famous.
He says Mr Halpin told him he had arrived in Goa a year after the 7th Earl of Lucan mysteriously disappeared in 1974.
Private investigator, Ian Crosby, runs a website devoted to tracing Lord Lucan's movements after his disappearance in 1974.
It offers $100,000 (£63,000) to anyone who can prove where the peer went.
He says the new information does not prove anything.
The book's authors said finding the Earl after his disappearance is outside of their remit.
"To be sure it was him we needed DNA. No one will ever have that. It was a case of building up evidence slowly but surely," said Mr MacLaughlin.
His co-author, William Hall, said the book is about trying to establish beyond reasonable doubt that "Barry Halpin" was Lord Lucan.
"We are claiming we have overwhelming evidence. We have not got proof because there is no body," he said.
Mr Crosby says he will not be paying out just yet.
Lord Lucan's blood-soaked car was found abandoned in Newhaven in 1974, the day after the battered body of his children's nanny
Sandra Rivett was discovered at the earl's family home in central London.
He was officially declared dead by the High Court in 1999 after investigations spanning more than two decades.
Casino owner and conservationist John Aspinall was one of the last people to see Lord Lucan alive.
He said in a 2000 interview Lord Lucan most likely committed suicide by scuttling his boat in the English Channel.