They go missing or their bodies are found at two different spots. The segments shows they are in a jeep during the night on some dark path off the road.

I believe this is the case you are speaking of. After a drought they found the jeep in a lake. Apparently they got lost and ran off into the lake and drowned.

http://unsolvedmysteries.wikia.com/wiki/Traci_Kenley_and_Bill_Rundle

Here I thought it was Arnold and Ruby (http://unsolvedmysteries.wikia.com/wiki/Arnold_Archambeau_and_Ruby_Bruguier):

I forgot about that case. It was strange the way they found them. Sorry I posted the wrong case.