The girl, who accidentally took her mother's weight-loss chocolate, was sent to hospital to get her stomach pumped in March. However, she died from an overdose of the appetite suppressant sibutramine following respiration and heart failure.
Her relatives called police, who later detected sibutramine in the girl's body, including her liver, urine and blood.
China has banned the production, sale and use of sibutramine in the country since 2010 due to its possibility of severe damage to the cardiovascular system.
Police later found that the poisonous chocolate was purchased by the girl's mother from the internet. They detained 34 suspects from 14 provincial-level regions and seized many illegal chocolate and pills.