after cadaver dogs found the scent of human remains on chris' car, detective brian wallace wasn't buying story. >> your story about what happened the night she disappeared -- total [ bleep ]. >> reporter: wallace pushed him for the truth. >> how did it happen? did she fall? is she dead? was she drunk as [ bleep ]? what happened? >> that's exactly it. we were struggling over the phone. and only this time we were outside on the steps. and -- she lost her footing. she fell. hit the step. and i heard the -- 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 -- >> no no -- >> reporter: new story? >> 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. >> got videos from the last 15 days. they've looked at everything from 10:00 a.m. to 4:00 a.m. your car never