Watch live: 9/11 memorial ceremony in Lower Manhattan

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. A look behind the scene