Joe Biden and Barack Obama will be in attendance as New York marks the twenty years since the September 11 attacks with a commemorative ceremony.
President Biden will also visit Shanksville and the Pentagon, and will be joined at Ground Zero in New York by Obama, whom he served for two terms as vice-president.
Many family members of the nearly 3,000 victims killed on that day are expected to gather at all three locations where the terrorists crashed the passenger jets they had seized that morning.
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