The mysterious origin of Covid-19 has given rise to many debates, allegations, denials and controversies. However, the entire history of biological threats and bio-weapons is full of such denials and allegations. Though classified as weapons of mass destruction along with nuclear and chemical weapons, the global arms race for biological weapons remained relatively inconspicuous. As evidenced by many historical examples certain features of Plausible deniability of bioweapons such as the covert nature, blurred boundaries of defensive and offensive research and ambiguity about the required set of equipment, resources, expertise and infrastructure make them distinctly different. Plausible deniability of bioweapons is a critical feature and needs to be a central theme while designing policies for credible deterrence and bio-defence.