A Chinese man was sentenced to life in prison Monday for poisoning dumplings that made four Chinese and nine Japanese consumers ill, in a 2008 incident, when Lu Yueting used a syringe to inject a highly toxic pesticide, that was reported to be methamidophos, into the frozen dumplings.

A court in the city of Shijiazhuang, about 170 miles southwest of Beijing, found Lu guilty of adding a poisonous substance to food, Xinhua News Agency reported. Lu was working as a temporary employee at the Tianyang Food Plant based in northern China's Hebei Province, and he was reported to have poisoned the food because he was frustrated with his colleagues and his income.

He was arrested and charged in China in 2010, and the plant was reportedly investigated by both Chinese and Japanese authorities, shortly after the incident took place, but they found no problem in the plant's production process. During his trial in July 2013, Lu confessed to his crime, stating that he felt sorry for the people who suffered from his action.

The news of Lu's sentence comes amid recent tensions between China and Japan over Japanese Prime Minister Shinzo Abe's visit last month to the Yasukuni shrine, which honors the war dead. The two Asian powers are also in the midst of a bitter territorial dispute over a group of islands in the East China Sea.

According to media reports, which cited Xinhua, the verdict was announced in the presence of officials from the Japanese embassy.