Have you looked at the IOSH guide 'Learning the Lessons' - downloadable on the Information and Resources tab? It may not have all the detail you want, but is a good starting point.

I suggest you need to identify controls from the point of the incident. Ensure the area is not disturbed when there is a serious incident or fatality where the police may be involved - except to make the area safe, in which case evidence should be preserved by photo or some other means. A senior manager should be appointed as incident co-ordinator as soon as is practicable. Any document will need to ensure that provisions are made for alerting and supporting staff in PACE interviews, trauma, and internal communications such as emails should be kept to a minimum with no flippant comments.