New York City officials say the unidentified remains of more than 1,000 people who died in the terrorist attacks on the World Trade Center will be preserved in a permanent memorial at the site, known as ground zero.

The officials say the remains will be stored at the planned memorial in the hope that science will one day find a way to identify them.

Investigators have been unable to identify the remains because in most cases the DNA was badly damaged.

Since the September 11, 2001, terrorist attacks, the medical examiner's office has recovered almost 20,000 body parts and tried to match them with nearly 2,800 people listed as missing. 1,271 victims remain unidentified.

Meanwhile, New York City is preparing to mark the second anniversary of the September 11 terrorist attacks with ceremonies to be led by the families of victims rather than politicians.

Other ceremonies are slated to honor those who died in attacks on the Pentagon and in rural Pennsylvania.