According to Saunders , the gunman said he was frustrated by the U.S. Postal Service 's response to an accident involving a postal vehicle .
Sheriff 's Department spokesman Chris Saunders said the man told them he was frustrated by the Postal Service 's response to an accident involving a postal vehicle .
The Dow Jones Industrial Average fell 0.7 per cent to 9,547.43 while the S & P 500 was 0.8 per cent weaker at 1,025.79 .