The article says that he found cigarette butts in the airplane. This DNA evidence would make it straightforward for the police to find the culprit if they wanted to.

Possessing someone's DNA doesn't automatically, magically tell you who they are. If there's nothing to match it to then all you have is someone's spit.

Except now, thanks to 23andme and other vast DNA database dragnets, an unknown person's DNA can be narrowed down to a few people based on their relatives.