And before that, they investigate based on less. That's how they find the rest................or not if it doesn't exist, but they don't know until they do the in depth investigation.
So... what's the goal of this investigation? The scientific relevance is, in the short to medium term, minimal. It will not actually lead us to better understanding of SARS-COV-2. It will not generate better outcomes for patients. It will not change the socio-economic situation in the world caused by the impact of the pandemic on our not-terribly-resilient systems.
I restate - this investigation looks like a blame game. For that, we need to consider the costs vs the benefits. If we find it came from the lab, the costs will include increased violence against out own citizens of Asian descent, and increased tension between China and the US. The benefit needs to be worth beatings, murders, and increase of consumer costs for goods pretty much across the board.
Better be a really good benefit.