Original sentence: On June 1 2005 he was appointed President of the World Bank Group, but resigned on May 17, 2007 (effective June 30, 2007), as a result of an investigation by the World Bank Group's board of executive directors, which accepted his resignation
Edited sentence: On June 1 2005 he was appointed President of the World Bank Group, but resigned on May 17, 2007 (effective June 30, 2007), as a result of an over six-week investigation by the World Bank Group's board of executive directors