biological weapon
A toxic or biological agent used with hostile intent — defined by intent, not amount
A biological weapon is, in international law, a means — typically a microorganism, a biological agent or a toxin — that has no peaceful application and that is constructed or used for the purpose of harming, infecting or killing humans, animals or plants. The concept belongs to public international law and is primarily regulated through the Biological Weapons Convention (BWC) of 1972, which prohibits the development, production and stockpiling of such weapons. It is therefore not a conventional physical weapon, but a biological or toxic substance used with a criminal, hostile intent.
In the context of bioterrorism and biological crime — as in the cases concerning ricin letters sent to American presidents and judges — the word denotes a poisonous biological substance used as an instrument of terror. Ricin is a plant-derived toxin extracted from the castor oil plant, and it is classified internationally as a biological or toxic warfare agent. It appears on lists of prohibited substances under both the Biological Weapons Convention and the Chemical Weapons Convention (CWC), because the boundary between biological and chemical toxins is in practice fluid.
Sending a biological agent such as ricin by post in order to target a state's highest officials — including a sitting president — is legally characterised not merely as an individual attack, but as an act of potentially bioterrorist character. In US federal law this leads to charges under statutes that specifically criminalise the possession and use of biological agents as weapons, reflecting the international obligation to criminalise such acts.
The international legal framework emphasises that a biological weapon is defined by the intent behind its use and the nature of the substance — not necessarily by the quantity. Even a small amount of ricin in a letter can constitute a biological weapon in the legal sense, because it has been produced or used with the intention of causing harm or making a threat. It is this broad, intent-based definition that makes the concept relevant in true crime contexts, where the perpetrator is not a state actor but a private individual.
