Agreed, if that was indeed Rick's friend then something else happend on the 8th, maybe nothing more than returning the Jeep to Moul's. It also would appear that our "cook" took care of the disposal alone.
Ricci had been digging on Jun 8 because he was all muddy. Maybe he decided he didn't have time because the cops would be coming back for an accounting of his time and he would be better off getting the Jeep turned in for the weekend so he would hopefully not have to explain the taking it out business. So he turned it in at 5:30 PM Saturday night and to left the burying job to his accomplice who the police had not interviewed and didn't seem to be after. I think he may have been nervously looking over his shoulder because of what they may have had in his friend's blue van.