EDIT: This post has been changed so that the estimated amount that Crooks backed up by is less than halfway from the crest of the roof to the back edge of the roof (he stayed in the top half of roof). The first estimates I gave were wrong. Wording has also been updated to be somewhat more cautious about details.
At the Butler rally, there were 10 total shots fired (I still have not been able to verify the claim that there was an 11th shot). The last two of the verified shots fired were taken by the protective detail for Trump — #9 by local protection (nonfatal to Crooks), #10 by Secret Service sniper (fatal shot).
Here is a video relayed by the Washington Post which keeps a running tally of the number of shots fired at bottom left:
Within the very first second of the video, the first shot is heard (and tallied at bottom left). Here is the tally after 7 seconds have passed:
By the 7th second after the first shot, the tally at bottom left shows nine total shots had been fired. The first 3 of them are grouped at the beginning, then a flurry of 5 shots are tightly grouped, then a 9th shot is fired at Crooks by someone from the protective detail. Also of note above is the vent sitting at the crest of the roof.
As a testimony to how shallow the angle on the roof was, that 9th shot — the first one fired back at Crooks — apparently came from the ground level:
After shot 9, and at right before the moment that Crooks got shot and killed by the 10th shot (the Secret Service sniper’s shot), he had repositioned himself back somewhat from the crest of the roof, where shots from the ground could no longer get to him (even though shots from rooftops still could):
[click to enlarge]
With a measuring tool, and the ridges on the aluminum siding of the building, there are an estimated 30 ridges worth of distance from the roof crest to Crooks’ “final” position before being shot dead. Crooks is visible at top left.
The angles might be deceiving us here, and throwing off our perspective, and Crooks may have only backed up by less than halfway from crest to back edge (staying within the top half of the roof). Here is an image which suggests that Crooks is backed up almost halfway back from the crest of the roof toward the back edge:
This screenshot, showing Crooks partially upright, coincides with the Washington Post report which said that the 9th shot caused Crooks to “temporarily recoil from his perch.” I interpret Crooks as partially upright at some distance from the roof crest — rather than him going partially upright right at the crest and exposing himself more.
NOTE: It should be noted that the Washington Post piece has conflicting reports and later on in that same report, instead of describing Crooks’ reaction to the 9th shot as a “recoil” we are told that the 9th shot caused Crooks to “slump over.” I’m making a choice to use the interpretation that matches the video above.
Even though there appears to have been a “recoil-and-repositioning” the helicopter footage in the aftermath reveals a body right up at the crest of the roof, with a rifle next to it:
[click to enlarge]
Here is an angle similar to where the footage was shot from, using Google Earth:
The Sky News article said that investigators were not allowed immediate access to the roof, because suspicious packages up there had to first be checked out by a bomb squad:
Did the bomb squad move the body?
By most indications, Crooks had repositioned himself away from the crest of the roof — to a new position somewhere up to halfway down the backside slant of the roof — but the body shown in the Sky News video shows a body right up at the crest of the roof, which is likely where he was before he repositioned.
No shots came from him for the next 10 seconds though (before the final shot, shot #10, took him out). If you don’t fire for 10 seconds, a likely explanation is that you don’t have a good angle. A likely explanation for not having a good angle is because you backed up.
If Crooks returned to the crest, as the helicopter footage shows, then you would have expected him to fire again within the next 10 seconds, because that — i.e., in order to get off more shots — is the logical reason that an assassin would return to a crest after having been shot at (while at that crest).
Reference
[Sky News article showing helicopter footage with body blurred out] — https://news.sky.com/story/donald-trump-shooting-video-shows-apparent-gunman-on-roof-13177673
[video showing Crooks’ after repositioning, set back somewhat away from the roof crest] — https://www.msn.com/en-us/news/us/trump-rally-gunman-stopped-firing-after-local-officer-shot-at-him/ar-BB1qToW3