The CIA is now trying to work out if one of the men who killed Berg was an important member of al-Qaeda.
Friends of Berg's family say he was the kind of person who liked to help people, and that was why he had gone to Iraq.
His family say he was planning to travel back to the US at the end of March, but was arrested by Iraqi police before being handed over to the coalition.
He was later released without any charge but was kidnapped before he was able to leave Iraq.
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