-- Police investigating the disappearance of a British bar girl have found remains of a woman's body encased in concrete 250 yards from the house of the prime suspect, raising new questions about the thoroughness of the police investigation.

Police said they were trying to determine if the body parts were those of Lucie Blackman, 22, who disappeared last July while working in a bar where foreign women are paid to entertain men.

Blackman's disappearance became an international case when her family, frustrated by the pace of the police investigation, mounted their own campaign to find her. Their effort highlighted the dangers for foreigners in the Japanese nightclub scene, and both British Prime Minister Tony Blair and Foreign Secretary Robin Cook made inquiries about the case.

While Japanese police have insisted their investigation was exhaustive, involving hundreds of investigators, each development has raised questions as to why it took so long.

The discovery today was in a cave south of Tokyo near the house of Joji Obara, 48, a wealthy Tokyo businessman who has been in custody since Oct. 12 and has been named by police as the prime suspect.

Police today declined to say why the discovery was made so close to the house four months after they allegedly conducted an intensive search of the property. At the time of their search, police knew Obara had purchased a boat and had been seen with concrete on his hands by an officer when Blackman disappeared, and today's discovery was made in a cave beside the Pacific shore a short walk from Obara's property.

Police recovered a torso, hands and a head that were encased in concrete, according to Japanese reports. Although police briefed Japanese reporters, they declined public comment "because no official announcement has been made," according to a spokesman.

Blackman's father, Timothy Blackman, told BBC television from his home on the Isle of Wight that "the assumption is that these are parts of Lucie's body, but really we have got to wait until that is confirmed or not confirmed by DNA testing."

Blackman and his ex-wife, Jane Blackman, have shuttled to Tokyo repeatedly, prowling the garish Roppongi district of "hostess bars" where their daughter worked, and plastering thousands of posters of the blond former flight attendant around the city. They offered a reward and opened a hot line, turning dozens of tips over to police.

They were initially circumspect about criticizing the authorities, although they acknowledged that they were exasperated as months dragged by and police insisted they had no leads.

Recently, however, Timothy Blackman ended his forbearance and blasted the Tokyo police as "corrupt," accusing them of "disgraceful and inhuman behavior." He charged that thousands of foreign women, many of them young travelers like his daughter who came to Tokyo to earn high pay in what they believed to be a safe country, were endangered because police ignored the crimes.

"This man and others like him are able to get away with these crimes for years . . . because the police have not acted," Blackman said in an e-mail message disclosed in the Independent newspaper in London. "He is rich. He is important to the club owners, so the police have let him get away with his crimes."

Obara has acknowledged that he met Blackman at the Casablanca Club where she worked -- for a drink, according to his lawyer -- but denied any involvement in her disappearance. He has said other bar women whom he is accused of raping had sex with him consensually. Obara's lawyers have protested that police are holding him illegally by issuing a series of other charges while questioning him about Blackman without charging him in that case.

When Obara was arrested for allegedly drugging another bar hostess and raping her, information emerged that Timothy Blackman contended pointed to police ineptitude or complicity.

Although police had said there were no suspects in the Blackman case, it emerged that Obara was well known to bar owners and to many of the women who worked in the bars. He has now been served with a warrant holding him on suspicion of raping five women by allegedly spiking their drinks with a drug to render them unconscious.

If convicted, Obara would be one of Japan's biggest serial rapists.

One woman, an Australian, died in 1992 after allegedly being drugged. According to reports from police in the Japanese press, Obara paid part of her medical bill and even met her bereaved parents, representing himself as the dead woman's recent fiance. Police have yet to say why Obara was not identified as a suspect in her death.

Police also said they could not trace a final call Blackman made to her roommate, although when Obara was arrested, police said the call was made from a mobile phone belonging to him.

They also have not said why they did not focus on Obara when the caretaker of one of his properties became suspicious of his activities around the time of Blackman's disappearance, and called police. A policeman visited Obara and found him with concrete on his hands, according to reports, and learned that he had purchased a boat in great haste. Still, he was not arrested until allegations were brought by another woman three months later.

Police officers carry a bag with remains found in a cave south of Tokyo. They were believed to be those of Lucie Blackman, who disappeared last year.