"Those terrorists will, sooner or later, mount operations both in Europe and in the United States," says CBS terrorism consultant Rohan Gunaratna.
Police and intelligence agencies say Zarqawi's now powerful network extends from Iraq to Syria, Turkey, Chechnya and Europe, smuggling people through porous borders, using fake documents. As CBS News Correspondent Sheila MacVicar reports, it's a network that experts say will undoubtedly spread to the U.S.
A bug planted by Italian police in a Milan mosque in 2001 caught al Zarqawi operative explaining how the network is expanding: "We need foreigners. We have Albanians, Swiss, English. The important thing is that they are very cultured."
In Iraq, al Zarqawi is behind a wave of suicide bombings and kidnappings, but his group also has a deadly and practiced interest in poisons. Raids in London and Paris in 2002 turned up evidence Zarqawi cells were trying to make the poison Ricin, and planning to use cyanide. Intelligence analysts say this is a strategy Zarqawi could return to.
Arrests in Germany and Italy revealed the core of his network in Europe and elsewhere: men he had been in prison with, men he trained with in camps in Afghanistan and now, men recruited and smuggled into Iraq. People who deal in fake passports, collect money and wait.
"Today we see a new generation coming up in the ranks of militant Islamist terror," says Rolf Tophoven of the Institute for Terrorism Research and Security Policy. "These are young people, fanatical people."
It's a new generation with Zarqawi as one of its leaders.
"We have had good effect against his network, we're going to keep it up and we are going to take it apart piece by piece," says Gen. John Abizaid
But Zarqawi has been a moving target. He escaped Afghanistan, and so far, is surviving in Iraq. As he slipped into Iraq, he could slip out again and analysts warn, take his war to the cities of the West.