贝的努力救了朱令一命, this is a difference issue.
I have my sympathy to Zhu Lin. But I do not agree that Sun to be accused as the killer.
Evidence is Evidence. Regardless 特定的时间,地点,人物,性格,年龄等因素, no one have the right to 连续还原理解 and draw a conclusion only based on his speculation, without evidence.
If Li Tianle story does not show those evidence ( Li's requests for Thallium, and the found of Thallium in Li's house), do you think the police will arrest and charge Li? I do not think policu will charge Li if the only clue is that Li is the only person who has access to Thallium.