NEW YORK – Letters written by Helen Keller. Forty-thousand photographic negatives of John F. Kennedy taken by the president’s personal cameraman. Sculptures by Alexander Calder and Auguste Rodin. The 1921 pact that created the agency that built the World Trade Center.

Besides ending nearly 3,000 lives, the Sept. 11, 2001, attacks on the trade center and Pentagon destroyed tens of thousands of records, irreplaceable historical documents and art.

A decade later, dozens of agencies and archivists say they’re still not completely sure what they lost or found, leaving them without much of a guide to piece together missing history.

The trade center was home to more than 430 companies. Twenty-one libraries were destroyed, including that of The Journal of Commerce.

The Cantor Fitzgerald brokerage, where more than 650 employees were killed, owned drawings and sculptures that included a cast of Rodin’s “The Thinker” — which resurfaced briefly after the attacks before mysteriously vanishing again.

A library of U.S. Customs Service held documents related to U.S. trade dating back to at least the 1840s. In the same building were nearly 900,000 objects excavated from the Five Points neighborhood of lower Manhattan, a famous working-class slum of the 19th century.

Jan Ramirez, curator of the National September 11 Memorial & Museum, said there was no historical consciousness surrounding the site before it was destroyed.

“It was modern, it was dynamic. It was not in peril. It was not something that needed to be preserved,” she said.

“Now we know better.”