Original: Ma was the first performer on September 11, 2002, at the site of the World Trade Center, while the first of the names of the dead were read in remembrance on the first anniversary of the attack on the WTC.
Simplified: A year after the attack on the World Trade Center, on  11 September, 2002, he played his cello on the site of the building while the first of the names of the dead were read in remembrance.