Four people were arrested Wednesday in connection with the killing of a 21-year-old pregnant woman in Tokyo’s Ota Ward in February, police said.

The man registered as the victim’s father, Seiichi Matoba, 63, and three others are suspected of conspiring to stab Junko Uno to death at her home, the Metropolitan Police Department said.

The three other suspects are Matoba’s wife, Midori, 54, his son Akira, 30, and Akira’s wife, Li Lunrong, 30.

Police said Matoba was among the many Japanese children left behind in China as their families hastily fled the country during the final days of World War II. Known in Japan as “war orphans,” a large number of Japanese children were separated in this manner and raised by Chinese foster parents.

Police went on to say that Matoba helped Uno enter Japan from China in 1998, telling Japanese authorities that she was his second daughter. Midori Matoba is Uno’s aunt.

Uno married a Japanese man in December 1999.

“I had a lot of trouble helping her enter Japan, such as spending a considerable amount of money, but she got married without our knowledge and tried to sever ties with the Matoba family,” the police quoted him as saying. “We talked about killing Uno.”

Li also admitted the charges, saying, “My younger sister and I killed Uno,” according to the police.

The police have obtained an arrest warrant for Li’s 26-year-old sister, whose name has yet to be released.

Uno was fatally stabbed in the neck with a kitchen knife at around 6 a.m. on Feb. 17 at her home in the Higashi-Kamata district of Ota Ward, police said.

Investigators said Uno had given a total of more than 1 million yen in cash to the Matobas in return for their favors, and they are looking into possible monetary trouble between the victim and the suspects.