<Tr> <Th> Construction started </Th> <Td> August 6, 1968 </Td> </Tr> <Tr> <Th> Topped - out </Th> <Td> December 23, 1970 </Td> </Tr> <Tr> <Th> Completed </Th> <Td> 1972 </Td> </Tr> <Tr> <Th> Opened </Th> <Td> December 15, 1970 </Td> </Tr>

Who worked at the wtc complex on 9/11