MIAMI — Construction of the pedestrian bridge that collapsed and killed six people in the Miami area was behind schedule and millions over budget, in part because of a key change in the design and placement of one of its support towers. Documents obtained by The Associated Press through a public-records request show that the Florida Department of Transportation in October 2016 advised Florida International University and its contractors to move one of the bridge’s main support structures 11 feet north to the edge of a canal, widening the gap between the crossing’s end supports and requiring new structural design. The span’s signature, 109-foot-tall pylon was to be built atop a base at the span’s northern end.