That is why there are a very limited number of people who could know what happened at the arrival. Colin would be one, though he supposedly left right away- someone working at the farm who was in the right place at he right time would be the only other potential witnesses.
When you write a book you should not do what we do here. We typically don't credit well known things. In writing a book you should credit everything, you should footnote every factual claim you make with a source so the reader knows where you got the claim from and can evaluate whether to believe such source. For instance if Jeremy is a source of most of the book that surely should be noted but really it should be done with any claim.
In a legal brief to a court (among other legal documents) we have to do that. Any factual assertion must have the source of the claim in parenthesis after the sentence that makes the claim. So we have to cite an affidavit, trial transcript or other document for anything we represent to the court because we are not first person witnesses so can't make a claim ourselves we must attribute a claim to a source. We can't just make factual assertions ourselves.
I have ready hardly any books about the case - but I guess there are two
potential reason for perhaps reading them -
1) witnesses can only answer what is asked of them in court and they may wish to say something but not have the opportunity
2) there may have been people who were not called as witnesses who may want to comment about things - not necessarily evidence ,but to refute say for example a comment about someones character.
For example I am guessing that Freddie was not called as a witness ( statement read out) because of his "drug" connections -but having listened to the case he may have had more to say.
So some books could be "interesting" in that respect.