tonight we begin a new series in some of the most notorious and intriguing unsolved criminal cases in history. the story we begin with tonight is recent history, the murder on falcon lake on the border between texas and mexico. less than four months ago, tiffany hartley says her husband david was shot in the head by mexican bandits, she tried to save him, but couldn't and escaped on her jet ski. what she hasn't been able to escape are questions about what happened that day and rumors there may be more to the story. >> we heard a sheriff say if you wanted to take a polygraph test to back up the story he'd support that. is that something you'd want to do? >> possibly, but i don't really think i need to because i know my story and i know, you know, what the story is. but if, you know, that's what