AIG Says Unit Faces U.S. Criminal Probe  NEW YORK (Reuters) - The U.S. Justice Department has opened  a criminal probe into whether American International Group Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AIG.N target=/stocks/quickinfo/fullquote"&gt;AIG.N&lt;/A&gt;, the world's largest insurer by market value, helped a  major banking client move bad loans off its books, AIG said on  Wednesday.