可能是你记错了，或是误解老师的意思了。当定语从句修饰的先行词指人时，用the same…who…是很普通的用法。又如：

That’s the same person who came yesterday. 那就是昨天来过的那个人。

The caller is the same man who was here yesterday. 打电话的人就是昨天来的那个人。

你的句子翻译：

Police suspected that the same men who were noticed loitering in the halls were responsible for burglarizing the law office. 警察怀疑闯入律师事务所行窃的人就是被人看见在大厅里闲逛的人（即是同一个人）。

补充说一句：当定语从句修饰的先行词指事物时，有人认为要用the same…that…，不用the same…which，其实这也不绝对。如：

I want the same wine which I had yesterday. 我要我昨天喝过的那种酒。