Sorry I can not type Chinese here.
The Police did not have sufficient evidence, neither did anyone. All they had was speculation.
If we change the story of Li Tianle to the one similar to Sun,do you think the US police will arrest and charge Li?
If there is no evidence that Li Tianle had applied for large quantity of Thallium, and Thallium was not found in her house, there is no other evidence found to show that Li had given Thallium to Wang, just she is the only one who have access to Thallium in Wang's family and friends, the police will not arrest and chrage Li at all. They will do the same as Chinese police did to Sun.