the Boston Marathon was run over a course of only 40.6km

[jutfrank]

I have to agree with teechar. In the context of police examining a crime scene, I think 'go back over' does mean (or certainly could mean) 'review in detail', rather than 'cover the distance again'.

I'm not sure I understand what you mean by 'review in detail'. It clearly means they returned to the scene and searched it again. This time they found the guns.

The OP uses 'over' as an adverb

You mean the marathon example? It's a preposition there, with over as head of a preposition phrase.

Regardless, I don't think it's a useful comparison for GFL

I think it depends to a large extent on the individual learner. These two cases of over are just about similar enough to be compared, in my judgement. They both have the same basic sense of covering a space.