More than 4 million Iraqis displaced since U.S.-led invasion

When the U.S. invaded Iraq in 2003, Yaghdan Hamied, like many Iraqis, took a job with the coalition.

Hamied worked with Americans rehabilitating schools in and around Baghdad--but always kept this a secret from his friends, family, and neighbors.

"We destroyed anything related to the U.S. work--deleted numbers from our computer and from our telephones," said Hamied, who took detours and extra buses to avoid being followed from his home to the U.S. embassy complex.

Still, one morning in October 2006, Hamied found a note pinned to his front doormat that read: "We will cut your head and your throat and throw it in the garbage." He then found a severed puppy head in his garden.