During the 1990s, Zarqawi trained under bin Laden in Afghanistan. After the fall of the Taliban, he fled to northwestern Iraq and worked with poisons for use in potential attacks, officials say.

During the summer of 2002, he underwent nasal surgery at a Baghdad hospital, officials say. They mistakenly originally thought, however, that Zarqawi had his leg amputated due to an injury.

In late 2002, officials say, Zarqawi began establishing sleeper cells in Baghdad and acquiring weapons from Iraqi intelligence officials.

--ABC News (Hat tip Hobbs)