回复：哦，谢谢分享你的知识，如果没看见犯罪，但被警察问同学名字，必须回答吗？

It is a judgment call. Depends on the state law and whether the stealing is a grand theft or petty theft, you may have an obligation to answer the question. Remember 5th Amendment is crime specific and you do not have its protection under such circumstances as a witness.