I took the wording to mean some type of duct work or gutter.Ahhh, Crooks was also a ninja?
There's plenty of HVAC techs here including me. I've been on quite a few of buildings of this type. Climbing the ductwork is not possible in my opinion. Using the uni strut holding the lineset maybe? But it's not structural. It's usually just screwed to the sheet metal siding with self tapping screws. It's just there to keep the copper tubing in place and looking neat. The gutters on these buildings are not something that I would trust to hold my weight. I'd grab it like a drowning man would a life preserver if I was falling but not as a means to get me on the roof.
The bands around the duct maybe an inch and a half and are usually three to four feet apart in a vertical installation. Even if they were only two feet apart Crooks would have to be a rock climbing legend to have the finger strength to hold onto it.
I'm tracking with what you are saying about the lack of load bearing ability but I have gotten on roofs via ducts and gutters with 20 to 30lbs on my back a bunch of times.
Some of the guys that were smaller and in better shape than me could get on a 12 foot roof in about 30 seconds. (pissed me off)
We would do it during classes as a challenge and as a learning tool to adapt. I was 200 to 220 lbs at that time and while in decent shape was totally NOT the ninja. We may have popped a few fasteners but never had anything tear off the side of the building. For sure it was not good for the building.
I'm not saying this as any kind of proof that the shooter used this method. I'm just saying if my fat ass could do it, it is totally believable that his lanky ass could as well.