请各位帮忙解答以下英语问题,急!

请各位帮忙解答以下英语问题,急!
The inspector pointed out that on the morning of the murder,the 8 o'clock train did not run at all.主句谓语动词发生在从句谓语动词之前,明显是过去的过去,为什么从句谓语动词不用过去完成时?像类似的句子还有：He said that he arrived at work on time./ she asked him what time he arrived at the sation? 这些句子都是从句动作发生在主句之前,时态使用上却是主句和从句都是一般过去时,我觉得从句都应使用过去完成时,搞不明白,请学英语的朋友们帮忙解答.