they told me that they had arrested david shepard and mike dixon for my dad's murder. so it made the funeral slightly easier for us as a family because justice was on its way. what did you know about michael dixon and dave shepard, leading into that arrest? how much did you know. we knew absolutely nothing about them other than thomas michael dixon had dated richelle before my father. that is it. narrator: they soon would learn plenty about a twisted and devious plan that led to joe sonnier's murder. [music playing] coming up, double trouble from a very odd couple-- dr. dixon was very well educated. he had a successful business up in amarillo. david shepard, he was a con man. his life was just tanking. narrator: --when "dateline" continues. [music playing] do your dry eyes still feel gritty, rough, or tired? with miebo, eyes can feel ♪ miebo ohh yeah ♪ miebo is the only prescription dry eye drop that forms a protective layer for the number one cause of dry eye: too much tear evaporation. for relief that's ♪ miebo ohh yeah ♪ remove contact lenses before using miebo. wait

the friend's name was david shepard. detective johnson called him the next morning.hnson: and the first thing out of his mouth is that, "detective, you are wasting your time looking at dr. dixon. he is a very nice guy, and he has nothing to do with this." andrea canning: sure enough, shepard vouched for dixon. yes, he was at his house that night to pick up cigars. his alibis checked out, so-- zach johnson: they did. we had checked him out. "surgeries is where i was." we went to the restaurant to see if we could obtain a receipt from them. and he had also said, "i can even fax you the receipt that i was at this particular restaurant on this day and time." are you thinking, ok, he's probably not involved? yes. i didn't have anything to tell us that he was involved. andrea canning: a promising lead that went nowhere. detective johnson moved on. there were more people to investigate-- the women in joe sonnier's life. coming up. did joe's former dance instructor and girlfriend make a wrong step? zach johnson: according to richelle, the relationship had not ended on a very