You have to think of evidence a different way. Every piece of direct or circumstantial evidence moves the needle one way or the other. Some things are smoking guns, some just explains how the search was narrowed and that information helps remove reasonable doubt. If the perp wants to argue over the relative value of touch DNA, he’ll have that opportunity to fight the science or provide an alternative explanation. Either option is made less vital by looking at the other evidence. Ie: “okay Mr. K., you have testified that xxx is the reason your DNA is in the home, even pretending that’s true, why was your vehicle in the immediate vicinity of the home at 3:00am on the date in question? Why does your cell phone data show you in that area often? Mr. K, prior to invoking your right to silence, you made several statements to the police, at any point did you deny this crime? Or did you ask if anyone else was arrested?” Just examples of how you respond to the argument you’re imagining.

In the case you cite, there really is only one piece of evidence. This case is not similar to that or a classic “wrongfully accused” dateline episode because there is so little relation between the killer and the victims and we already know there is more evidence than simple DNA (even if we don’t know the extent). There is no witness ID, no accusation from anyone, no obvious motive that would draw attention. While the public doesn’t know the level of evidence, we can assume the cops moved the needle to “probable cause” with Elantra discovery + dna + suspect driving across the country. If they made an arrest on this alone, they’d still be in a good spot, but I’m confident they have much more and that’s why they moved quickly.

This is my long winded way to say,