If he’s the perp then this likely wasn’t his first violent act, you would think he would have some prior acts but may not have been connected to those by previous investigators.
Also would say if he is the guy, he’s no Einstein to have held on to that car, sooner or later the FBI would track down all 25,000 of them as reported earlier, and it would be fairly simple to eliminate 99.9% of them. Here’s somebody from the area and if there were 25,000 such cars nation-wide then the number in eastern WA and northern ID would likely not be much greater than 25. You would obviously start with those 25 before paying a lot of attention to cars in Texas or Florida. That of course assumes that his driver’s licence or car ownership data had any mention of Pullman WA and not PA. But there would be other overlaps.
LEO probably asked campus police at Idaho and WSU to check their parking permit records.