– “…we do not believe that any type of laboratory-based scenario is plausible.”
I don’t see what this claim is based upon. Some research involves cycling the subject virus through multiple generations of cells of a specific species. All that does, basically, is speed up natural selection, so how would anyone tell the difference? Maybe the key word in that sentence is “believe”; not a scientific term!
I’m well out of fields I’m familiar with on this subject, but a friend of mine has been following the virus-tracking forums etc. for years. Something he points out is that the usual animal species chosen for testing because of their close relationship to humans – monkeys for obvious reasons; ferrets for their respiratory system; etc. – are not used for SARS-CoV-2, because SARS-CoV-2 doesn’t multiply well cell-to-cell within such hosts. Instead, transgenic mice have to be used. Such mice have been genetically modified to include human cell lines, and are used as laboratory test animals. (Transgenic mice were the source of the antibodies Trump was treated with.) If SARS-CoV-2 seems well adapted to such transgenic mice, that would seem to be another indicator of possible lab origin.