A US woman has been added to the list of those killed in the attack on the World Trade Center, after dying from dust generated by the towers' collapse.
Smoke and dust lingered over Manhattan for days after the attack
New York's chief medical examiner said he was certain the dust contributed to Felicia Dunn-Jones' death from a rare lung disease five months after 9/11.
The toxic cloud contained particles of asbestos, lead, glass, and cement.
The ruling that she was the tragedy's 2,750th victim may have implications in the cases of dozens of other deaths.
Hundreds more people, including those who have helped clean up Ground Zero, say they continue to suffer from respiratory problems because of breathing in the toxins.
Ms Dunn-Jones worked as a lawyer near the World Trade Center when suicide attackers crashed two hijacked airliners into the buildings.
After the towers collapsed, she ran through the thick clouds of dust which swept through Manhattan.
Ms Dunn-Jones developed a cough and had difficulty breathing four months later, and died on 10 February 2002.
An autopsy showed she died of sarcoidosis, a disease which produces microscopic lumps called granulomas on lungs and is often associated with exposure to environmental hazards.
In a letter made public on Wednesday, New York's chief medical examiner, Dr Charles Hirsch, said he was certain "beyond a reasonable doubt" that the dust "was contributory to her death".
Dr Hirsch said he would amend Ms Dunn-Jones's death certificate accordingly and change the manner of death from natural causes to homicide.
Her name will be added to the official list of victims from the attacks on New York.
The 9/11 death toll, not including the hijackers, also includes 184 killed when a plane flew into the Pentagon and 40 killed in a hijacked plane that crashed into the ground in Pennsylvania.
In another development, years of legal wrangling over the insurance claim for the World Trade Center has finally ended after insurers agreed to pay a total of $4.5bn dollars to rebuild Ground Zero.