Re amateur and formal investigation; there is both opportunity and need for two forms (or levels) of ‘investigation’.
Formal investigations are often constrained by considerations beyond the ICAO guidelines e.g politics, practicality, experience. Many of these reports fail to explain why an accident occurred, or insufficiently to provide specific safety solutions. This might be due to the lack of data or inability to understand the human activity from the available recordings. Any resultant safety activity in the latter case would be speculative. I believe that these limitations also apply to why-because (W-B) analysis.
An alternative (amateur) analysis is valuable when conducted by operators and individuals who ask ‘could this happen to me’. The process of thinking about an accident has safety value; it can be equated to a safety audit on a specialist subject. This is also somewhat speculative, but can occur more quickly while the event is fresh in peoples minds (greater training effectiveness), and can be more proactive in looking ahead to avoid a similar accident, as opposed to a formal report of how to avoid the accident we have just had.
The value of the audit can be greater where specific details of the situation and activities leading to the accident are known, hence the need to publish ‘public’ data (not all data) quickly and without comment. This process can be aided with use of web forums and appropriate ‘eye-witness’ reporters; and even with some erroneous data the safety activity of thinking about the situation would not be significantly compromised.
The difference between the two; – a formal report has accountability to a higher authority (usually government).
A safety audit, thinking about safety has accountability, but this is within the operation or directly to the individual providing professional development; perhaps of far greater value than formal reports.