were looked upon as potentially as threats. yes. as threats. and that s why they were given instructions to go ahead and shoot at them. reporter: the sheriff now tells cnn that eyewitnesses have come forward to him. witnesses he says who claim to know what happened here that day. they describe a military-style attack. three boats, several shooters, and hundreds of rounds being fired at two jet skiers. the shot that killed david hartley was an unlucky shot. reporter: the sheriff now believes the killers were instructed to kill tiffany hartley, too. what happens next, he says, is a scenario he has put together from three witnesses on the mexican side of the lake. one source in mexico and at least one witness who told cnn that he saw a high speed chase on the u.s. side. a boat chasing a girl on a jet ski. it is clear that one of sheriff gonzalez sources was involved
the jet ski was destroyed. my understanding, the jet ski was taken apart. that parts that would float were burned and buried afterwards. and the parts that would not float were just thrown into the lake and of course, they sunk. this here is coming in from mexico. reporter: the sheriff believes hartley s story but may never be able to prove it. david hartley s mother can barely control her emotion. what happened to david and tiffany was an act of terror. plain and simple. it was a senseless violence, but it was an act of terror. and that is not going to end at the border. it s over here already. reporter: and for tiffany herself, it is even more troubling. reporter: do you think your husband is a victim of, in a way, politics? i would say a victim of terrorism, of politics, and, um,
reporter: but there was some unfinished business. one last adventure david had long talked about, but never got around to. he had heard of a church partially submerged in falcon lake on the mexican side in an abandoned village called old guerrero. perfect for a couple who loved their jet skis and loved adventure. i m just like, okay. let s go see it. reporter: had they asked local law enforcement would have warned them about pirates on the lake. had they asked, captain stacy holland would have told them not to go. we don t recommend going into mexico on the side of the lake, but it s perfectly well within your rights, but we just want you to be aware that that threat is out there, and it s very real, and you should take it seriously. reporter: it was a thursday and david hartley called home. they were excited to go have one last big ride on their jet
reporter: david hartley had always been interested in visiting the sunken church in falcon lake. on thursday morning, september 30th, 2010, a week before he and his wife would move home to colorado, david decided they would go. did you know then what you must know now, that there had been several attacks on that lake? that fishermen don t cross into mexico on that lake anymore. we did know there were attacks. we didn t know where they were exactly. reporter: you had no worries whatsoever when you took those jet skis out? no idea. as tragic as this is what i think i m hearing from you is what the hartleys did was incredibly stupid. incredibly. reporter: fishing guide and resort owner speedy colette says business on the lake has taken a beating since the hartleys made what he called a stupid trip to
we ve had, along the border, shootings. we ve had, along the border, murders, home invasions, burglaries, rapes. all types of crime where it s associated with what i call spillover violence. reporter: siggy gonzalez was the sheriff of zap ata county, texas and oversaw the investigation of the hartley incident. he has retired since our interview. i remember when i started as a deputy sheriff back in the 1970s, where this was used for drug trafficking. human trafficking. being used like that forever. reporter: and lately, even before the hartleys trip to falcon lake, gonzalez says a new threat has emerged. pirates. totally inaccurate. definition of piracy a lot different than what i know it to be. had one robbery on the lake totally.