3 Top Officials Leaving Citigroup -- Memo  NEW YORK (Reuters) - Three senior Citigroup Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=C.N target=/stocks/quickinfo/fullquote"&gt;C.N&lt;/A&gt;  executives are leaving the company, after being found partially  responsible for last month's forced closure of Citigroup's  private bank in Japan, a person familiar with the matter said.