There were several viable suspects if Ringo was murdered, and there was at least one confession to it of which I'm aware which is considered dubious by western historians.
Wyatt and Doc were supposed to be in Colorado at the time and this is confirmed by contemporary newspaper accounts. Historians have considered the various means of transportation available at the time and compared it to the timeline of events. They consider it possible that Wyatt and Doc could have made the trip but not likely.
Ringo's grave is still in the middle of nowhere part way between Tombstone and the ghost town of Galeyville. The question I have about the incident is how long it would have taken to FIND Ringo, and the probability that noted characters like Wyatt and Doc could have returned to the Tombstone area without being detected.
Ringo was mentally unbalanced and publicly threatened suicide on more than one occasion.
Hollywood fast draw has always looked good, but I've wondered just how fast it was with an original Colt. Hammer springs on those period guns are heavy, a reflection on the primers of the day.