朱令案中有两个奇怪的人物， 一个是协和的李舜伟，另一个是清华的薛方渝。
协和的李舜伟水平并不差，他看到朱令的第一感觉就是铊中毒， 但奇怪的是随后就在没做任何检测的情况下几乎马上排除并且坚决抵制，直到朱令父母在外面有检测结果。在UCLA的网上有记录：

/9/95 Dr.Shunwei Li, Chairman of Dept. of Neurology at PUMC, made a
conjecture of thallium poisoning. But his guess was not put to
scientific test and soon was denied by some famous toxicologists
in Beijing. Since then, they had not consider that possibility.
,,,,

4/28/95 It was such a group international suggestion of thaliium
poisoning that made Zhu Lingling's parents brought some
samples for test to an independent agency, Beijing
Institute of Preventive and Occupational Medicine.
清华的薛方渝也很奇怪，首先他出具清华无铊的证明，其次他拒绝封锁现场的理由，虽然这些可以用维护清华声誉来解释。但其后的结果却很奇特。清华无铊的证明导致了协和的李舜伟放弃铊中毒的可能，如果不是贝的介入，朱令就死于无名疾病。拒绝封锁现场导致了奇怪的宿舍盗窃案，把投毒嫌疑人牢牢锁定在孙维声上。
如清华的薛方渝同协和的李舜伟素不相识，很难把薛方渝同投毒嫌疑人联系在一起。但朱令大舅妈的陈述却指出＂双方是老朋友"，这大大提升了薛方渝投毒嫌疑人的可能性。
如果排除了孙维，薛方渝是最可能的投毒嫌疑人