This is the most perplexing thing of all. This person made absolutely no attempt to hide. It's a very confident thing to do, and to me it says this person was never worried that this truck would be identified. They had to assume they would be seen on cameras. They were in fact caught on camera, coming and going from the scene that morning, and looking around the night before.
To me this means it had no plates at the time of the murder.
Even if you think of the scenarios where I could get a vehicle that had no linkage to me on paper, even with many degrees of separation, each degree is linked to the last and eventually police get close enough to figure it out.
This is what is bothering me- it is most likely someone she knew, who owns or has access to a truck like that, who knew her schedule to the minute that morning, and had a beef with Liz; and not a single person in her sphere can think of anyone who that description might fit?