A mother in Japan has filed a lawsuit against the police, alleging that the unlawful arrest and detention of her 16-year-old daughter contributed to the teenager’s death months after she was released from custody.

The case concerns a teenager identified by the alias Runa, whose mother is seeking 109 million yen in damages from Hyogo Prefectural Police. The lawsuit alleges that authorities failed in their responsibility to protect the girl during an 18-day period of detention in 2025.

According to CNN, the teenager was arrested on June 17 last year over an alleged assault at a care facility run by her mother for people with special needs. Her mother said Runa had tried to prevent an agitated resident from biting others. The teenager denied the allegation and was never charged.

During her detention, Runa reportedly stopped eating and repeatedly wrote about wanting to see her mother. Prosecutors obtained a court-approved restriction preventing her family from visiting her, citing concerns that evidence could be interfered with because her mother operated the facility.

Her mother said she was not fully informed about the extent of her daughter’s deteriorating condition, despite raising concerns and seeking information about her meals.

Runa reportedly collapsed shortly before her release and was taken to hospital. When her mother was finally reunited with her, she said the teenager was severely weakened and had become almost unrecognisable.

After leaving custody in early July 2025, Runa continued to lose weight and was diagnosed with post-traumatic stress disorder. Her family said she became fearful of adults, including medical professionals, making it difficult to persuade her to receive further treatment.

She died about five months after her release, weighing approximately 20 kilograms. Her death was attributed to malnutrition associated with an eating disorder, according to CNN’s reporting.

The lawsuit seeks to establish whether the arrest and detention were lawful and whether the authorities’ handling of the teenager’s custody contributed to the fatal deterioration in her health. Hyogo Prefectural Police declined to discuss the individual case, saying the matter was before the court and that the prefecture’s position would be presented during the proceedings.

The case has intensified scrutiny of Japan’s criminal justice system, particularly its practice of holding suspects in police custody for extended periods while investigations continue. Critics refer to the practice as “hostage justice,” arguing that prolonged detention and interrogation can place significant pressure on suspects, including those who have not been charged.

Japan’s Juvenile Law states that the detention of minors should occur only when it is unavoidable. However, legal experts cited by CNN questioned whether holding Runa for more than two weeks, while restricting contact with her mother, was necessary and proportionate given the circumstances of the allegation.

The case also raises questions about safeguards for young suspects, access to family members and the responsibility of authorities to monitor the physical and psychological well-being of people in custody.

Runa’s mother said she hopes the court proceedings will establish the truth about her daughter’s treatment and help prevent similar cases in the future.

The allegations remain the subject of legal proceedings, and the lawsuit will determine the state’s responsibility for the teenager’s detention and subsequent death.