Humans don't have to bioengineer a weaponized virus on purpose for a lab to be what created the virus. One common thing that happens in these research labs is that viruses can jump from one lab culture to another and swap genetic material to make hybrids that are more contagious for example. This might explain the furin cleavage site in the spike protein that helps SARS-CoV-2 pry its way into human cells.

Further reading here: https://www.technologyreview.com/2021/03/18/1021030/coronavi...