but after cadaver dogs found the scent of human remains in chris' car, detective bryan wallace wasn'the night she disappeared is total bull [ bleep ] >> reporter: wallace pushed him for the truth. >> how did it happen? did she fall? she did. was she drunk as [ bleep ]? what happened? >> that's exactly it. we're struggling over the phone, only this time we're outside on the steps. and she lost her footing and she fell and hit the step, and i heard the crack. >> he said they were struggling over a cell phone. she slipped, fell backwards and hit her head and died. >> reporter: did you believe this new story? >> no, no. no way. >> reporter: 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've got videos from the last 15 days. they have looked at everything from 10:00 a.m. till 4:00 a.m., and your car never even pulls on the lot. >> reporter: chris then changed his story an