Or that there was a jug of water kept in the car (not as likely in Iowa because of the need for antifreeze in the winter, but this was summer), because the cooling system leaked (common in older cars, especially with plastic and aluminum radiators)...and that CR was naked (for obvious reasons) when he did the deed in the cornfield...and that he had a knife with him because he worked a manual job (I used to never leave home without one). You work with what you have at the time.
Once, in rural Louisiana, my pick-up was over heating, and I had to pull over. What to do? I kid you not, as I sat there in the middle of no where (pre cell phone days), I looked out my passenger side window and there was a pipe with a faucet sticking up out of the ground on the edge of a corn field! I kept the engine running, filled my radiator and my now empty water jug, and rolled onto Alexandria. The heck with Oscar's Razor, at times weird stuff happens, and the breaks go your way, even for opportunistic killers.
However, I do see your point. Rest assured that video of CR's car turning to follow MT should (hopefully) be enough proof of premeditation to convict CR for Murder 1 on the State level. If that falls through...
I still think that the Fed's could still file their own list of charges if they felt a need to do so. CR committed payroll fraud by working and paying Federal payroll taxes under an assumed name, even better if CR even sent anything through the mail to do this. This Federal crime (if the Malibu was owned by his employer) gave him access to the car used in commission of the murder. Federal murder charges carry the death penalty. Overeaching by the Feds? Maybe, but there is at least one Ex-Con Louisiana governor who can tell you how creative the Feds can get with filing charges. And who knows what the Feds could dig out of the Patirot and Homeland Security Acts passed since the turn of the century.