Reaching that conclusion is pretty simple. At least simple and straight forward enough to charge someone. Probably not as simple to get an actual conviction.

I think this is what happened. They probably found several cigarette butts inside the perimeter of the vandalized private property, they ran DNA tests for all of them and one matched this guy's DNA. There are only a few possible reasons for his DNA to be inside that perimeter:

1) He was a contractor doing work for the Dakota Access Pipeline operator (probably already ruled out, otherwise he wouldn't have been charged).

2) Somebody took his butt from outside and put it inside the perimeter (very unlikely).

3) He actually smoked that cigarette and dropped the butt in that location while he was vandalizing it (most likely scenario from the prosecution point of view).

4) He trespassed the property at a different time and smoked and dropped the cigarette butt at that time. This is still an unlawful behavior but is probably better than all the other charges. (This is a possible scenario but it would be pretty hard for his defense to demonstrate this is what actually happened).

Again. This is enough for prosecutors to charge this guy but it doesn't mean at all that this is good evidence to get a conviction. In my humble opinion, a cigarette butt with your DNA is pretty weak evidence in this particular case.

So you’re saying, no problem, all he needs to do is prove his innocence?

This specific incident a bunch of people were around the equipment. Presidential Candidate Jill Stein was there and took a can of spray paint and painted the scoop of one of the bulldozers with an activist slogan. The incident is on film and was widely covered by the media. That was the vandalism. These bulldozer scoops have a rough life and any graffiti on them wears off within hours of their next use so the assertion that this was legitimate damage is questionable. It's known and documented on film exactly what happened there on that day. It's also known that only a tiny number of people engaged in bulldozer graffiti, the particular people who did were filmed, and their identities are known. The person named in the affidavit was not among any of the people who were seen painting the bulldozer scoop. Furthermore nothing observed there would be reasonably described by any rational person as "rioting", which is the charge being levied with this butt being the only evidence presented.

If he had an alibi for (3), then (4) would be plausible to show.

Yes, that's true. 4 is not that unlikely actually. He could have trespassed with no intention of doing harm. We don't know how the location looks like, but it's possible that it was just an open construction job site, so trespassing would have been as simple as just walking in.

That's why I posted it - using DNA to prove trespass seems wildly disproportional to the gravity of the offense, while being insufficient to prove participation in any more serious crime.

>2) Somebody took his butt from outside and put it inside the perimeter (very unlikely).

Only if you discount squirrels.