>> it was hard for me not to tell anna. i couldn't. you have to balance the integrity of this investigation. you don't want it jeopardized. >> all thomas could do was file the results away and try to find more evidence against denis. but as the years slowly ticked by one by one, nothing. finally in 2007, a decade since wendy vanished, thomas decided if she wanted to get closer to denis to find out what he knew once and for all, she would need some help. >> that's when we looked at passing it off to the unsolved homicide unit. >> vancouver's "e" decision, to be exact, the premier cold case unit in british columbia. get ready for an undercover mission unlike any you have ever seen. coming up -- the sting by investigators worthy of the big screen. >> they're described as rated