not account for him anywhere. >> reporter: that gap was crucial because it was during that time frame that police believe the murder happened. they even traced the route they thought nathan might have taken that day from the starbucks to the park, a quick walk to his house, then back to the starbucks to see if he could have done it in time. >> 6 minutes 55 seconds. >> reporter: not only possible, they said but probable. more likely, they figured, than a stranger breaking into the house during the roughly 20 minutes denise was out. >> it's inconceivable to think that somebody breaks into the house the exact same time, runs through the house, finds a lock, pries it open, loads it up, hides behind the door, to execute her. that just can't happen. >> reporter: something else that didn't make sense, they said, was that denise's car was not in her driveway. after the murder they found her silver ford here in this nearby park.