The National Science Foundation released a video that shows the 60-year-old Arecibo Radio Observatory's collapse.
From Ars Technica:
As you can see from the video, the drone was examining the area where the cables looped over the support towers. Specifically, it was examining the tower that had supported the one main cable that had failed earlier—note that one of the gaps that the cables pass through is unoccupied. While it was filming, individual wires in the cable started snapping, and the cable failed completely shortly afterward. The remaining connection visible there, which was connected to the scientific instrumentation, survived a bit longer before the plunging platform pulled it apart.
In the second segment of video, the view from the visitor's center shows how the failure of the cables at that tower affected the rest of the system. With one of the three support anchors gone, the instrument platform dropped toward the dish in between the remaining two. This created off-axis forces that caused the tops of those towers to be wrenched off the rest, resulting in about 60 feet of reinforced concrete plunging to the ground below. At the same time, backstay cables that ran from the tower to the ground came loose and swung around wildly.