Perhaps you should try some spelling variations:
"september 11 -- terrorism attacks, 2001" » "september 11 -- terrorist attacks, 2001", "september 11 -- terrorist attack, 2001", "september 11 -- terror attacks, 2001"
"september 11 -- terorist attacks, 2001" » "september 11 -- terrorist attacks, 2001", "september 11 -- terrorist attack, 2001", "september 11 -- terror attacks, 2001"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"september 11 -- terrorism attacks, 2001\") OR (\"september 11 -- terorist attacks, 2001\"))~".
• Removing quotes may allow a broader search: (( september 11 -- terrorism attacks, 2001 ) OR ( september 11 -- terorist attacks, 2001 ))~.
• Adding a wildcard symbol may retrieve word variants: (("september 11 -- terrorism attacks, 2001") OR ("september 11 -- terorist attacks, 2001"))*.