reporter: so based on your sources and your intelligence, when they began to encroach on what would be a drug deal, they 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
just a warning to let people know that this threat is out there and it s very real and that we ve had documented cases of pirating. so it s mainly for situational awareness, and, you know, we don t recommend going into mexico on this side of the lake. reporter: tiffany hartley says she had heard about troubles on falcon lake, but she and david had been there once before and things were fine. she never thought that somehow anything could happen. we hadn t heard of anything for a while and we were just there in august. enjoyed three, four hours that day on falcon lake. reporter: after all, it was so sunny. so calm. so perfect for one last ride. i told him, please, don t shoot. please, don t. reporter: in an instant, tiffany hartley claims she and david were caught in a war zone.
where was the camera they used to take pictures of old guerrero? why wasn t there far more blood evidence? the jet ski 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 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
see a sunken church. he is sick of the media attention and insists that the lake and the fishermen are completely safe as long as they follow these unwritten rules. this is not a jet ski lake. never a jet ski seen. they come, they show up on jet skis that they don t see, then they try to approach them and stop them, because it s a war over there. two cartels fighting each other for control, and they don t stop. they take off running. colette agreed to take us to old guerrero, eight miles into mexico, into what he describes as a drug war, to show us just how safe it really was. but before he even passed the channel marker dividing the u.s. and mexican border, speedy made us promise not to raise our camera, not to raise any suspicion and told us there s no doubt how jet skiers would look following this same path, like drug smugglers.
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 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