>> reporter: in the case of david hartley, that includes the cartel inflicting its own investigation and its own brand of justice. security expert fred burton has followed the case closely. >> it's my understanding that the individuals that were involved with the killing of mr. hartley were in essence picked up and killed by the zetas themselves. >> reporter: the killers were killed? >> correct. the killers were killed by the organization, because, remember, this is bad for business. >> reporter: if the killers are dead, tiffany hartley may never be able to prove what happened. she knows how many people still don't believe her story. and she and david were just sightseeing, that she tried to save him. that she outran boats with gunmen firing at her, in interviews she remains unemotional.