Investigation
The scene: arriving and securing it
What the first person there does, in order, and why almost all of it is about not doing things.
Principles from published manuals, not procedure. What has to be done at a scene is set by the law of the country you are standing in and by the orders of the service you belong to; where those differ from this, they govern.
Lessons
This material is education, not certification, and it does not replace accredited professional or medical training. It describes how the association works; it is not legal advice and confers no powers.