The father of murdered British woman Lucie Blackman said his daughter had been robbed of justice yesterday after a court cleared a Japanese businessman of involvement in her death.

After a long fight, the family of Ms Blackman listened with disappointment as Joji Obara was acquitted of all charges relating to the 21-year-old from Kent, who disappeared in July 2000 while working in Tokyo.

The former British Airways flight attendant's dismembered body was discovered in a cave near Obara's apartment seven months after she vanished.

The prosecution alleged Obara drugged and raped Ms Blackman before she died, then chopped her body into 10 pieces and encased her head in concrete at the property developer's luxury apartment.

Despite being cleared of involvement in Ms Blackman's death, the 54-year-old was sentenced to life in prison at Tokyo District Court after being convicted of a series of rapes and the death of Australian woman Carita Ridgway.

Ms Blackman's mother, Jane Steare, said yesterday from her Kent home: "I'm heartbroken, absolutely heartbroken. I just can't believe this verdict. My worst fears have come true."

Ms Steare, the executor of Ms Blackman's estate, later added: "This aching void in my heart feels like it will never go away, but I truly believe that one day we will hug each other again.

"I love you so much and always will. Your mummy will never give up hope of finding justice and the truth."

Other member's of Ms Blackman's family, her father, Tim, and 27-year-old sister, Sophie, were in court and told of the verdict by an interpreter.

Speaking to reporters in Tokyo, Mr Blackman argued prosecutors had failed to present some evidence in court. "I'm afraid to say the lack of justice for us today has been the failure of the prosecution team to develop the case adequately," he said. "There is nothing that will change that Lucie is dead, but in many respects Lucie has been robbed of her justice."

Matt Searle from the Lucie Blackman Trust said: "This is not what we were expecting." Mr Searle said he had heard the 1600 days Obara has already spent in jail would be deducted from his sentence.

He added that he understood prisoners given a life sentence in Japan could be eligible for parole after 10 years.

Miss Ridgway, 21, a drama student who also worked as a bar hostess in Tokyo, died of a drug overdose after being raped by Obara in 1992. But her case was not linked to the businessman until Ms Blackman's disappearance eight years later.

Another two of the rapes Obara was convicted of involved foreign women he met at Tokyo hostess clubs.

Ms Blackman's father, who has led a campaign to secure justice for his daughter, has been criticised for accepting £450,000 from a friend of Obara.

His ex-wife, Ms Steare, accused him yesterday of "colluding with the defence team" and acting like Judas by accepting "blood money". Mr Blackman described her comments as "absolutely, entirely inappropriate".

Defendants in Japan who admit their guilt can pay compensation to their victims or their grieving families as part of the court process and as a way of expressing remorse. Judges take the payments into consideration when passing sentence. The family of Miss Ridgway rejected Obara's offer of £200,000, but he is believed to have paid £10,000 to at least one of his rape victims.

Yesterday's verdict comes as Japanese police continue to hunt the killer of a British woman whose body was found in a sand-filled bath at an apartment outside Tokyo last month. Language teacher Lindsay Hawker had been beaten and suffocated. Police are still looking for the prime suspect, Tatsuya Ichihashi, 28.