A proposal for Sino-Japanese co-operation in criminal investigations has been welcomed in Japan, but human rights groups are concerned about the death penalty. Officials from both nations have agreed to consider an agreement that would enable the sharing of information and the repatriation of prisoners convicted abroad. The proposal - rare amid tense Sino-Japanese ties - can be linked to the murder of a family of four in southern Japan two years ago. Three Chinese students were charged with killing Shinjiro Matsumoto and his family in Fukuoka and stealing 40,000 yen ($2,800) before dumping their bodies in Hakata Bay. Wei Wei, 25, was sentenced to death in Fukuoka District Court on May 20. In January, a Shenyang court sentenced Yang Ning to death, while Wang Liang was jailed for life at the Intermediate People's Court in Liaoying. Yuichi Kaido, secretary-general of the Centre for Prisoners' Rights Japan, said: 'The two countries have been discussing such measures ... but the Fukuoka case may have made the matter more urgent. We welcome these initiatives because under the principles of social rehabilitation a prisoner should be held in his home country.' Mr Kaido said he hoped any treaty would be based on similar legislation drawn up by the Council of Europe, which allows prisoners to refuse repatriation if they fear unduly harsh treatment. He also said China carried out the death penalty - which his group strongly opposed - far more frequently than Japan. Makoto Teranaka, director of the Japanese branch of Amnesty International said: 'We must make sure that prisoners who are returned are not tortured or subject to the death penalty.' About 1,690 Chinese nationals were held in Japanese prisons at the end of last year, while there were believed to be 11 Japanese in Chinese prisons.