Wei Wei, a 40-year-old Chinese national, was at a detention center in Fukuoka on Thursday, after being on death row for more than 16 years, Justice Minister Masako Mori said.
While he was living in the country on a student visa as a language student, Wei Wei was convicted alongside two other Chinese accomplices of murdering Japanese clothing store owner Shinjiro Matsumoto, his wife, and two children in Fukuoka.
After killing the family, Wei and his two accomplices then weighted and handcuffed the bodies and dumped them into Hakata Bay, Mori said at a news conference.
He had pleaded guilty to all four murder counts, but maintained he was not a central figure in the case, reported SBS News.
Japan has maintained the death penalty despite growing international criticism, and currently has more than 100 prisoners on death row. This figure includes 84 seeking retrials, according to the justice ministry.
Mori said she signed off on Wei’s execution “after careful consideration,” in light of the international anti-execution movement. She explained that as a law-abiding country, Japan carries out its executions based on the country’s criminal justice system.
“It is an extremely cruel and brutal case in which the happily living family members, including an eight-year-old and 11-year-old, were all murdered because of truly selfish reasons,” she told reporters.
Wei’s two accomplices were tried in China, where one was sentenced to death and the other was given life imprisonment, according to Japan’s Kyodo News agency.
A relative of the murdered Fukuoka family told NHK that “the only feeling that remains is sadness.”
“We were finally able to think of happy times when the four were alive after many years have passed since the incident, but today’s execution only brought back painful memories,” he told the broadcaster.
Amnesty International said the hanging showed Japan’s “shocking lack of respect for the right to life.”
“The country has shown that it lags far behind most of its peers,” Arnold Fang, an East Asia researcher for the group, said in a statement. He noted that more than 100 other countries have abolished the death penalty.
Japan and the United States are the only two countries in the Group of Seven advanced nations that retain capital punishment. A survey by the Japanese government showed an overwhelming majority of the public supports executions.
Executions are carried out in high secrecy in Japan, where prisoners are not informed of their fate until the morning they are hanged. Since 2007, Japan has begun disclosing the names of those executed and some details of their crimes, but disclosures are still limited.
Since Prime Minister Shinzo Abe returned to power in 2012, his government has executed 39 people. Last year, Japan hanged 15 people, including the guru of the Aum Shinrikyo cult and 12 former followers convicted in a deadly Tokyo subway gassing.
Some lawmakers, including governing party members who oppose executions, recently launched a group to promote public discussion of the death penalty.
The Associated Press contributed to this report.