This problem of the truck sticks with me. Whoever did this had no regard for the truck being seen or identified (seemingly). Obviously it would be easy to check if anyone remotely close to Liz had such a truck registered now or in the past, or anyone at the same address as someone close to her. In what circumstance would you have access to a truck where you would have no care if someone saw it because it could never be traced back to you? My first thought is you stole it but what else? It could be unregistered, could be from a dealer lot with no plates, I could work for a rental company, I might have access to a fleet for property management or construction.
My guess is that it was definitely a rental or stolen, or they took the plates off.