The recent discovery in London and Paris of small amounts of what is thought to be ricin, a lethal toxin that is one of the most deadly of natural poisons, appears to indicate that terrorists are actively preparing to cross a new threshold by using chemical and biological weapons. These developments have intensified the hunt for one of the key figures believed to be behind this threat, a Jordanian Bedouin known as Abu Masib Zarqawi (real name thought to be Ahmed Fadil Nazal al-Khalayleh). Zarqawi heads a small organisation called Al-Tawhid, which appears to have cells operating across Western Europe...