And answering it in detail is giving tools to people who may want to do it.
"releasing a very transmittable and deadly respiratory virus with long incubation period" is just one of many ways.
It seems to me like demanding an exact explanation of how AI would build a bioweapon is like demanding to know exactly how a nuclear war would start before deciding that nuclear weapons are a legitimate concern. We can imagine many scenarios, but whatever we imagine is very unlikely to be the exact set of circumstances and events that lead to the catastrophe. Is the issue here that you can't imagine a bioweapon being created? Aren't there several labs around the world already working on viruses ? Aren't there existing bioweapons? And facilities capable of manufacturing them? If humans have access to those places and AI can communicate with humans, then that's all you need.