The problem is not that the Chinese don't allow for a real investigation. Most of the information is in the public domain, like the scientific papers about the gain-of-function research and the funding by Pentagon fronts. The missing parts could be unearthed by asking the intelligence community. Problem one is that the intelligence community will not incriminate themselves. The second problem is that blaming the Chinese too much will provoke counter moves that will expose the role of universities in US and Canada and the aerobiology specialists from Fort Detrick.