There are lights down at the intersection, but no lights on the exit ramp between where you exit Hwy 20 and turn left to go to Sac City or right to go north to where the truck was found.
Someone could have stopped David, blocked his path, ect further up the exit ramp from the lights where it would have been dark, but still far enough away to not create a suspicious scene from vehicles passing by on Hwy 20. Not that there is a lot of traffic at that time of night.
Given the "Porch Light" on the trailer someone could have known it was David a fairly long ways away if he was targeted. Especially if someone knew David should be rolling down this ramp at a certain time.
JMO
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