and i we heard the -- we heard the crack. >> he said they were struggling over a cell phone, she slipped, fell backwards and hit her head and died. did you believe his story? >>, no no way. >> finally, chris admitted heather was dead. but insisted it was only an accident. still the most important evidence was missing. heather's body. chris told detectives he dumped her at a gas station, police went there, found nothing and checked security cameras. >> they got videos from the last 15 days. they have looked at everything from 10:00 a.m. to 4:00 a.m.. your car never even pulse on the lot. >> kiss chris then changed the story and told somebody to get rid of the body. >> i jokingly asked, hey, you want to make a couple hundred bucks. >> no, no, chris, stop. this isn't working. that's crazier than the first one. >> four hours into the interview, wallace sensed chris was out of stories and out of options. so the detective game him one last chance.