Relatives of a Sri Lankan woman who died while in custody at an immigration center in central Japan last year sued the government on Friday, demanding 156 million yen ($1.35 million) in damages.

The family of Ratnayake Liyanage Wishma Sandamali alleges she was illegally detained and died due to a lack of necessary medical care. The suit was filed with the Nagoya District Court two days before the first anniversary of her death.

Ratnayake Liyanage Wishma Sandamali's younger sister Poornima holds Wishma's photo as she speaks to journalists in front of the Nagoya District Court on March 4, 2022, after filing a suit against the Japanese government over the Sri Lankan's death last year while in custody at an immigration facility. (Kyodo)

Wishma died at the age of 33 on March 6 last year at the Nagoya Regional Immigration Services Bureau after a month of medical complaints, including vomiting and stomachaches.

The Sri Lankan arrived in Japan on a student visa in 2017 to study the Japanese language but overstayed her visa, with her asylum application denied by immigration authorities.

Her immigration status was discovered after seeking police protection in Shizuoka Prefecture for domestic abuse in August 2020 and she was sent to the Nagoya immigration facility to await deportation.

Her request for provisional release, which supporters say could have helped her, was denied.

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Almost three months after Wishma's younger sisters flew to Japan, the Immigration Services Agency of Japan said in an investigative report issued in August that the immigration center staff lacked awareness on handling crises, and that there were problems with the facility's medical and information sharing system.

The report also said Wishma died of illness, but that an investigation could not determine the precise medical cause because there were multiple elements that could have triggered her death.

"We still don't know why and how she died. I did not think it would take this long," her sister Poornima, 27, told journalists in front of the district court on Friday.

In November, the relatives filed a criminal complaint with the Nagoya District Public Prosecutors Office against the immigration center's senior officials, saying Wishma's death was caused by a lack of medical care. The prosecutors later accepted the complaint.

On Friday, Justice Minister Yoshihisa Furukawa told reporters, "Etching remorse deep in our hearts, we will make continuous efforts so that (a similar situation) will never happen again."

"This is something that must not happen at immigration centers, which are responsible for lives," he said.