Some things (going by memory here) that seem to support the hypothesis:
1) Major point of differentiation for this virus is that compared to it's closest known relatives, it has acquired a furin site (eukaryotic protein cleavage site) that enhances its virulence.
2) That furin site RNA contains a non-canonical amino acid codon
3) That non-canonical codon contains a restriction site that could easily be used to track, whether, say, your added furin site is surviving multiple cell passages, by performing a restriction digest and running the fragments on a cell.
Like I said above, it's circumstantial, but this is all very normal. Both adding the furin site (how does coronavirus evolve into something more virulent?) and tracking it that way. Then all it takes is someone to get infected (EVERYONE working in biology has broken at least one lab safety rule in their life, even in BSL4) and either not be symptomatic and realize, or not say anything.
I describe the evidence in detail in this detailed longform post I wrote on reddit a few months back: Hi, I have a PhD in virology focused on emerging viruses, and a few months back I wrote a very lengthy and involved piece full of sources.
And in there, I describe exactly how wrong your point 1 is. And how misguided your point 3 is.
The post also won a "best of r/science 2020" award!
You can find it here: https://www.reddit.com/r/science/comments/gk6y95/covid19_did...
See under "Addendum to Q2"
What about the CCPs long track record of cover ups and lies instills you with confidence that there isn't a top-down effort to coverup a possible lab leak?
If the CCP wants a cover up, then the scientists under their employ will probably lie. Very few would be brave enough to be publicly truthful in such a situation.