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LOWER MANHATTAN (PIX11) — Sunday marks 21 years since terrorists hijacked four planes, crashing two of them into the World Trade Center in Lower Manhattan.

Nearly 3,000 people were killed and thousands more injured on New York City’s darkest day. In the more than two decades since, cancer and other health issues have claimed the lives of many others who were exposed to toxins around ground zero. Those maladies continue to afflict first responders and civilians.

Family members of 9/11 victims gathered Sunday morning in Lower Manhattan to read aloud their names and honor a vow to never forget.

The program included moments of silence to mark certain events of 9/11, starting at 8:46 a.m. when the first plane crashed into the World Trade Center’s north tower.

In addition to relatives of the deceased, officials were in attendance at the somber commemoration. Vice President Kamala Harris was among the dignitaries who attended.