Jaba and others - If you were a witness to the event, get some time alone and recall clearly what you saw and heard, and write it down in detail, forgetting nothing.
You know you'll be questioned as part of the investigation, it's important to set in stone what you saw and heard, before too much time elapses, and other events start to intrude on the memories.
What makes it worse, is that much time elapses before coroners hearings and perhaps even lawsuits occur, thus making the potential for your memory to forget important small things.
If you do happen to become ensnared as a witness in a lawsuit (God forbid), aggressive lawyers will try and make you see and hear things you didn't hear or see, and thus put doubt in your mind.
Having a written witness observation to refer to, put down on paper from the day or two after the event, helps to ensure that no-one can put doubt into your mind over the sequence of events, or what you actually saw or heard.