I wanted to address this both in terms of walkaway and foul play.
First, foul play: The most likely scenario in this case is that RFG was planning a romantic encounter. He would meet a woman, possibly the Mystery Woman, and spend the night with her. This was planned; they would get lunch, shop, or just walk around. They were together and something happened.
They had an argument the became physical. Or, RFG fell down a flight of stairs. Or, RFG has a heart attack. Whatever happens, the woman, hides the body. Maybe she is married and doesn't want her husband to know. Maybe she is or was a defendant, a key witness, or a relative of either, and she is worried about the effect. So, she hides the body.
Second, walkaway: The helper lives in Centre County (which is very likely if there is a helper). The helper purchases a car and drives to Lewisburg on 4/15/05. Helper gives it to RFG, but the helper is now 50+ miles from home. RFG knows that the Mini Cooper and possibly the laptop will be found in Lewisburg and that he was seen on the same day; he has to take the helper back to Centre County, but he wants to appear that he was in Lewisburg.
RFG does not want to draw attention to this helper and have LE show up and ask the neighbors if they saw him with the helper. So, he drives the helper back to the helper's house and spends the night. He drives back to Lewisburg on 4/16 and makes sure he is seen, on foot, in the SoS. Then he gets back into the car helper brought the day before, and drives off.
Third, the witnesses are wrong: Bennett is a respected business owner with a degree from the Wharton School at Penn. He is credible, but that does mean that he, or his two employees are right.
At least 6 people saw him in Lewisburg, some in the Mini and in the lot, on the afternoon of 4/15. They are independent, i.e. they were unknown to each other, but the corroborated what some of the others were seeing. Plus, the physical evidence, the Mini and his scent in the parking lot, could have been in place from 4/15. There is not that evidence for RFG being in the SoS on 4/16.