Homes claims he was able to identify a video camera based on its metadata embedded in the youtube footage. However, videos are transcoded when uploaded to youtube and any original camera metadata is lost.
The view through the rifle scope shows the jumpers from the side before either attempted to deploy his chute, so very high up the building. That would put the sniper equally-high in another building. But when Holmes surveys the dead jumper, the sniper is said to have been in a bush a few feet from the jumper's body, which would have fallen straight down after being shot. So the sniper would have seen the jumper from directly below - not from the side. And that would also have been the easiest place from which to make the shot since the jumper would be falling directly toward the bullets.
It makes no sense for the shooter to even try to shoot the base jumper before his chute deployed. In free-fall, he is moving fast and accelerating quickly, making him very hard to hit. Also once the chute deployed, he would slow down abruptly, another way to miss if the shooter took his shot too early. The logical thing to do would have been to wait for the main chute to slow down the target.
When Holmes shows Bell the pilot chute, he explains that BASE jumpers use that system to deploy the main chute. But when the suspect explains how the trio lost its first member, he says the jumper was unable to deploy his main chute because he was unconscious. That's one way the pilot chute is safer - unconsciousness causes the release of the pilot, deploying the main.