Lucie murder suspect and a sinister plot to smear her name

Lawyers for property developer Joji Obara offered thousands of pounds for details of 21-year-old Ms Blackman's confidential health records.

They also demanded background information on her and on her family's "reputation".

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The lawyers claimed the inquiries were part of a legitimate investigation into the Blackman family for a business deal.

It was only after the British private detectives discovered the Lucie Blackman they were investigating was the woman killed in Tokyo in 2000 that the lawyers admitted they were acting for the man facing trial for her murder.

Solicitors from the Maki Attorney Office in Tokyo began making their inquiries into Lucie's family and friends in September 2004.

The requests came ten months after Obara first went on trial for her murder. Hearings were held just one day a month which meant it was not until last month that the Not Guilty verdict was announced.

In phone calls and emails, which have been seen by this newspaper, one of the firm's lawyers, Yukihiko Ozawa, instructed UK investigators to begin a search into the backgrounds of five people, including Lucie and her parents Tim Blackman, 53, and Jane Steare, 52.

They were also asked to examine the backgrounds of Louise Phillips, Lucie's best friend who had travelled with her to Japan, and Louise's sister Emma.

Mr Ozawa asked that the investigation "should cover employment history, academic background, hobbies, human relationships (friends, associates etc), family members and marital status and reputation".

Over the following weeks the firm became impatient to know how the inquiries were going and began to ask for more detailed information: "Can you make investigation about Lucie Blackman's disease history? We only know her dental hospital and dentist's name."

The UK investigators on the case became suspicious. They wrote: "This does not appear to be a due diligence enquiry."

After two months, the investigators wrote again: "We were not initially aware that this was a murder enquiry.

"A number of aspects in our investigation have therefore changed...I would appreciate confirmation that your client is Joji Obara."

The lawyers admitted their client was Obara, 54, and the investigators immediately stopped their inquiries.

Last month Obara was dramatically acquitted of killing bar hostess Lucie, of Sevenoaks, Kent, whose dismembered body was discovered buried in concrete in a cave near his luxury apartment.

But he was jailed for life for eight rapes and one manslaughter.

Katsura Maki, senior partner at the law office in Tokyo, said: "Three years ago I was approached by a man who wanted information on a number of individuals, including Lucie Blackman and her family."

The lawyer refused to confirm the client was Obara.

Sources close to the Blackman family called the news "sinister".