This wasn't a biological weapon.
Gain of function research was being carried out for the benefit of society (or resume padding). However, it wasn't subject to oversight (to put it mildly) and was being handled by a lab ill-equipped to do so safely.
China has massive zoonotic reservoirs. The US researchers that led the world in Coronavirus study wanted to do gain of function, but couldn't do it domestically and didn't have access to the wild novel coronaviruses.
Money and notes changed hands, and the Wuhan lab went about gain of function research. The lab was sloppy, the modified virus leaked, and the rest is history.
There are probably only a handful of people ultimately responsible for this. The individuals from the US writing the proposals and pushing for it despite lack of safety, and those in China that knew the risks but went ahead. (The coverup and slow responses are also to blame for the spread.)
Millions of deaths out of lack of oversight and desire for personal prestige. That's the story.