A 23-year-old Chinese man has made a detailed confession on how he and two accomplices murdered a family of four in Fukuoka in June, slayings that police suspect may have been a drug-related contract hit.
Wei Wei, a former student, was arrested on suspicion of fraud and robbery on Aug. 8.
Last week, two Chinese men wanted in connection with the slayings told police in China, where they are in custody, that they were involved in the killings, sources said.
Wang Liang, 21, and Yang Ning, 23, also former students in Japan, returned to China shortly after the murders were reported by the media in late June.
The handcuffed bodies of Shinjiro Matsumoto, a 41-year-old clothing merchant in the city of Fukuoka, his 40-year-old wife, Chika, and their two children were found June 20 at the bottom of Hakata Bay. The corpses had been weighted down by dumbbells.
Police have learned that Matsumoto had been growing cannabis at an apartment in Fukuoka's Chuo Ward, about 4 km from his home.
He went to the apartment on the evening of June 19, hours before he was killed, to tend the plants, police said.
Police believe the three Chinese men were hired as killers by someone who knew about Matsumoto's activities.
Wei told investigators how he and his accomplices had broken into Matsumoto's home and killed the family, police sources said.