Thallium

— Used as a poison, thallium is a colorless, tasteless substance that can be fatal in doses of as little as one gram.

— Thallium was initially suspected in last year's fatal poisoning in London of former Russian security agent Alexander Litvinenko.

— For poisoning purposes, thallium would be in a powdery or crystallized state.

— Thallium as a poison works by knocking out the body's supply of potassium, essential for healthy cells, and attacking the nervous system, the stomach and kidneys.

— Thallium's effects are not immediately noticeable and frequently take weeks to kick in; symptoms include hair loss and a burning sensation in extremities.

— Thallium has been used in rat poison in the past, and it is still used to make lenses, semiconductors, dyes and pigments.

— Thallium was used by Saddam Hussein, who poisoned several of his Iraqi opponents. The CIA also reportedly considered using thallium against Fidel Castro.

Source: Associated Press