The MAIB
If you want to see this sort of thing done well, go read on of the Marine Accident Investigation Board's accident reports (http://www.maib.gov.uk/home/index.cfm). The primary goal of these --- which is printed in large letters at the top of every report --- is to determine what happened and how to stop it happening again. Also --- and again, this is printed in large letters --- the reports are inadmissible as evidence in any judicial proceeding that's attempting to apportion blame.
The reports themselves are a miracle of brevity and clarity, stating clearly and simply what happened, what went wrong, and what needs fixing. They're also not shy about pointing out the mistakes people make, but the point is always that people always make mistakes, and the system needs to be designed to cope.
I recommend them to anybody who wants to see how an accident report should read. (I gather it's possible to subscribe to a tiny four-page flyer containing summaries of the accident reports; I've seen them, and they're fascinating reading, but have been unable to find this on their website.)