During the late 1980s and early 1990s Obara invested heavily in real estate speculation. After losing his fortune when the bubble burst and his firm collapsed, he reportedly used his business as a money laundering front for the yakuza syndicate, Sumiyoshi-kai.
His pornographic video collection, 4,000 to 5,000 of which were recovered by police, led police to believe that Obara may have raped anywhere from 150 to 400 women. A recreational drug user, he was reported to an obsession with Caucasians and developed a sex fetish for molesting unconscious women. Police found over 200 sex videos involving Obara molesting women in this manner sometimes wearing a facemask and report that his extensive journals made reference to "conquer play", a euphemism describing his sexual assaults on women he wrote were "only good for sex" and on which he sought revenge, "revenge on the world drugging them with chloroform.
Blackman's mysterious death and disappearance, as well as Obara's trial, received high press coverage in Japan as well as internationally — especially in the British media. As a result of the publicity surrounding the case, three foreign women came forward to describe waking up, sore and sick, in Obara’s bed, with no memory of the night before. Several of them, it turned out, had reported him to the Roppongi police, but had been ignored.
On July 1, Lucie went on a dohan (a paid date) with a customer from Casablanca. No one heard from her again. The Blackman family, wanting to find Lucie flew to Tokyo and took the opportunity to start a high-profile direct media campaign, including approaching British Foreign Secretary Robin Cook who was in Tokyo at that time. Newspapers started publicizing Blackman's disappearance on July 13, when British Prime Minister Tony Blair made mention of the murder during an official visit to Japan where he met with Prime Minister Junichiro Koizumi. Blackman's case received enormous coverage in British and Japanese media and an information hotline was staffed by British ex-pats, a reward of £100,000 made by an anonymous businessman.
On January 10, 2001, Blackman's dismembered body was found, buried in a shallow grave under a bathtub in a seaside cave at Miura, Kanagawa, about 30 miles south of Tokyo, just a few hundred meters from Obara's apartment. The body had been cut into eight pieces. Her head had been shaved and encased in concrete. The discovery of the body was too late to determine the cause of the death. The verdict by three judges cited the lack of forensic evidences as a reason for acquittal. Some foreign media criticized the police.
A Trust promoting personal safety was established in her name.
Obara has maintained his innocence, claiming the drugs that caused her to die were self-administered.
Tim Blackman, Lucie Blackman's father, accepted £450,000 in mimaikin—or condolence money—from a friend of Joji Obara. The other members of the family were against the acceptance of the money.
Evidence supporting his guilt in regard to charge of rape included the approximately 400 videos he took in which he engaged in date rape activities. For the charge of manslaughter of Carita Ridgeway, the prosecutor produced an autopsy report showing traces of chloroform in Ridgeway's liver and a paper trail showing that the accused accompanied Ridgeway to the hospital before she died. In Blackman's case, however, the prosecutor could not produce any forensic evidence linking the accused to her death. Even the cause of her death could not be determined, as discussed below.
The judge stated that in deciding on the sentence he did not attach much importance to Mr Obara’s payment of “consolation money” to a number of his victims.
The Japanese judicial system has received some criticism for its handling of the case. It is believed that the police did not take this missing person case seriously "because Lucie was working illegally in a job from which women often flee without notice". As a result, the discovery of the body came too late to determine the cause of the death. The verdict by a panel of three judges cited the lack of forensic evidence as a reason for acquittal. Some foreign media from common law countries also criticized the police for having leaked information in the case to the press that could cause a mistrial. However, as Japanese civil law system does not use juries, this cannot be grounds for a mistrial.
Former prosecutor Takeshi Tsuchimoto, now a professor of criminal procedure law at Hakuoh University Law School, criticized the decision to acquit Joji Obara for the murder of Lucie Blackman by pointing to the conviction of Masumi Hayashi due to circumstantial evidence.
The public prosecutor has appealed the Blackman-related verdicts and on March 25, 2008 an appeal trial commenced in the Tokyo High Court.