Police arrested Junko Nakano on suspicion of setting fire to a warehouse. She said she was twice stripped, her genitals were searched and she was interrogated for up to 10 hours a day for 23 days in succession.
"You can't imagine the humiliation of being treated worse than a dog, having a police officer hold onto your handcuff and watch while you go to the bathroom," Nakano said.
The 30-year-old insurance saleswoman refused to confess despite what she called psychological and physical intimidation by police and investigators.
Nakano was released on insufficient evidence after being held for the maximum pre-indictment period allowed by law.
Haruo Katayama, an official at the National Police Agency's detention control division, said Nakano had been arrested and released but would give no details of her treatment.
"It is our policy not to discuss specific cases," he said.
Twenty-three days is the longest pre-indictment police custody period allowed among industrialized countries, most of which permit four days or less.
The average pre-indictment custody period in Japan is 15.6 days, according to the National Police Agency. Suspects are often sent back to police custody even after their indictment. Judges have issued extensions of more than 100 days.
Nakano's case provides an insight into the shadier side of law enforcement, Japanese-style. More than 2 million people are detained each year in Japan's police cells.
"Police in Japan use threatening tactics to extract confessions, and the whole procedure remains hidden from public scrutiny and unquestioned by the government," said Yuichi Kaido, an attorney with the Japan Federation of Bar Assns.
The pillar of the system is Japan's prison law, passed 82 years ago and left unchanged to this day. The law, originally passed to remedy prison overcrowding, sanctions the temporary use of police cells to detain criminal suspects.
Critics say prolonged custody in the hands of police invites abuse of suspects, particularly because they are entitled to a public attorney only after being indicted. This keeps a cloud of secrecy over the interrogation process.
Human rights organizations attack the Japanese police custody system, also called the substitute prison system, as a flagrant violation of United Nations human rights principles.
Amnesty International's secretary general, Ian Martin, spoke to lawyers in Japan recently and appealed for reforms in Japan's police custody system. "Every detainee should have immediate and unrestricted access to a lawyer. It is unfortunate that Japan does not grant this much," he said.
Japanese law restricts visits with attorneys to infrequent 15-minute sessions that must be cleared by a judge.
Martin also called for the separation of detention and interrogation authorities to ensure more neutral treatment.
He met with Ministry of Justice officials to request an official response to appeals for reforms made by Amnesty International last year. Both parties declined comment on the talks pending a formal response from the ministry.
The Justice Ministry said several prisons need to be replaced but money is tight. Skeptics say that is ironic, given Japan's economic condition. Even some politicians question the logic.
"If there is a shortage of prisons in Japan, it is because the government is not interested in building new ones," said Keiko Chiba, 42, a socialist member of the Upper House who once defended criminal suspects as a private attorney.
Attorney Kaido and other lawyers are drafting a bill that would abolish the substitute prison system and guarantee prompt and unrestricted access to a public attorney. They plan to submit the bill to the government next year at the earliest.
The Justice Ministry and National Police Agency have several times over the last few years submitted a bill that would give police cells legal status as permanent custody centers, but it has never been passed by Parliament.
"Police cells are necessary custody facilities, as they make the interrogation and investigation process swifter and more convenient," said Shunichi Furuta, specialist in legal affairs at the Ministry of Justice's correctional affairs division.
But the bill would not change the 23-day custody period or the restriction on public attorneys, and critics charge that it would not address the issue of police maltreatment of suspects.
Patience with legislative channels has run out for many former detainees who have lost friends or jobs after being branded as criminals despite false charges.
About 100 women recently staged the first organized street demonstration against sexual harassment and other forms of police brutality. They halted traffic and drew silent glares in a bustling Tokyo shopping district while blaring songs about police-instigated rape and torture.
The event's organizer, Chisako Tezuka, 47, was arrested three years ago on suspicion of fraudulently obtaining a loan. The former Buddhist nun was held for 20 days before being released when police discovered she had repaid the loan 2 1/2 months before her arrest.
She said that during her detention she was twice genitally searched, interrogated for eight to 10 hours a day for the first 10 days while handcuffed and tied to a chair, and forced to urinate in front of male officers.
Another official at the National Police Agency confirmed Tezuka's account of her arrest, release and two body searches but gave no further details of her detention.
One search was done at the police station and another at the detention center, the official said, because "she behaved as though she might commit suicide and could be hiding something in her genitals."