In software you would never do a postmortem without understanding the root cause of the incident. If this was caused by a lab leak, or even gain-of-function research, that seems like a pretty important detail.
This incident has cost millions of lives and possibly undone decades of progress on reducing poverty worldwide. It is worth pursuing multiple angles in parallel.
Put it this way, if the cause of the worldwide pandemic was because it leaked from a lab then you should fix the lab.