Sorry, I couldn't find pricing data for that day. The closing price for the S&P 500 (GSPC) on September 28, 2012 was $1,440.67. It was down 0.4% for the day. The latest price is $6,746.55.
DATE
OPEN
HIGH
LOW
CLOSE
VOLUME
September 28 2012
$1,447.13
$1,447.13
$1,435.60
$1,440.67
3,509,230,000
Daily pricing data for the S&P 500 dates back to 12/30/1927, and may be incomplete.