Coming home the other day I tried to make note of the trucks I saw. A lot of Toyota's and Ford's. Then some Dodge's and Chevy's. Only one or two Nissan's and none of them black or Pro-X's. OK, granted this not Texas. But I was just trying to get an idea in my area. I can't imagine that LE hasn't gone to the TX DMV and obtained a list of all black Nissan Frontier Pro-X within, say, a 50 mile radius of the crime scene. So, someone is either currently from outside the area or had access to a truck from outside the area? Or LE can't make a connection from the owner to Elizabeth because he was hired?
The hired killer. To me this looks so much like that except one aspect. Why? Per everything out in the media, neither Elizabeth or her husband were involved in the drug trade and don't appear to have associated with the wrong class of persons. The only remote possibility is Elizabeth's work. She worked for a company that inspected pipelines - not in actual inspections but in an administrative capacity. I have to suspect that pipeline inspections involve EPA regulations. But if anything large enough to motivate someone to kill Elizabeth would seem to be something that could be found by looking at inspections through a period of time prior to the murder.
I haven't ruled out the aspect of a hired killer because it appears to strongly indicate that point. Elizabeth's hobby with the Star Wars and Harry Potter probably had her crossing paths with persons outside the Houston area and this was personal. This killer could be from San Antonio, Austin or Lake Charles LA, just for a few examples. If from even farther away like Dallas-Fort Worth, Shreveport LA or New Orleans LA they might have spent the night or nights somewhere. The last couple of times I spent out of town in a hotel they didn't ask for any info on my vehicle so checking hotels within a day or two ride to Houston may not yield anything. And sometimes even when you provide vehicle data to a hotel it is not entered in the hotel's system - i.e., the data is only on the registration form.