What I'm surprised about is the bullet casings and markers left at the site - wouldn't professionals remove those?
Inanimate objects in an isolated rural area getting shot up around spring break (April 16th) smells a lot like underutilized youths with a case of beer being destructive. Road signs, substations, the Alaska Pipeline [1] - if it's rural enough it all gets shot up sooner or later.
If it's disruptive enough, and you're in a position to benefit from spinning up the facts into conclusions that earn your responsibilities some funding, then why shouldn't it be terrorists because some casings didn't have fingerprints.
[0] https://duckduckgo.com/?q=casings+catcher
[1] https://en.wikipedia.org/wiki/Trans-Alaska_Pipeline_System#I...
It's not all that far from the spaghetti neighborhoods, but that's where the weird stuff happens. Cranky rural folks break things at the encroaching edges of development. Bored kids get a couple of miles past streetlights and sidewalks and feel like it's no-mans-land.
Perhaps professionals would be less likely to remove casings because they do not expect to ever go to trial, or know that the gun they used can not be connected to them (because perhaps it was issued to them for this job), are not local to the area or do not intend to remain in the US after the job.
Only 100 casings were found, which does not strike me as very much... Basically just three people dumping a mag each + a smidge extra.
It is interesting that the article mentions only finding 7.62x39. This kinda says non-NATO to me, or at least the shooters want us to think "ruskies!"