. >> reporter: massachusetts state police investigator, tony delucia. >> i pulled back the dress from her throat. i saw a severe wound to her neck. >> reporter: lauren astley was found with a bungee cord tangled in her hair. >> nate is definitely not involved in this. >> nate would never do something like this to lauren. like, that is absurd. >> reporter: on the night of july 3, after lauren went missing, police officers talked to nathaniel and his mother, beth, three times, and each time they told essentially the same story. nathaniel was home alone when lauren stopped by for five minutes, but she never got out of her car. the story seemed credible. >> we wanted to know the comings and goings of lauren and nathaniel in the days and weeks prior to this event happening. >> reporter: investigators would learn in the weeks prior to lauren's murder her ex-boyfriend nathaniel's behavior had changed. his uncle, george mattingly: >> well, he had gone from a kid who was always on the move, always working out, to a kid who was basically at home, lying on the couch, looking miserable. >> report

. >> reporter: massachusetts state police investigator, tony delucia. >> i pulled back the dress from her throat. i saw a severe wound to her neck. >> reporter: lauren astley was found with a bungee cord tangled in her hair. >> nate is definitely not involved in this. >> nate would never do something like this to lauren. like, that is absurd. >> reporter: on the night of july 3, after lauren went missing, police officers talked to natha anielnd his mother, beth, three times, and each time they told essentially the same story. nathaniel was home alone when lauren stopped by for five minutes, but she never got out of her car. the story seemed credible. >> we wanted to know the comings and goings of lauren and nathaniel in the days and weeks prior to this event happening. >> reporter: investigators would learn in the weeks prior to lauren's murder her ex-boyfriend nathaniel's behavior had changed. his uncle, george mattingly: >> well, he had gone from a kid who was always on the move, always working out, to a kid who was basically at home, lying on the couch, looking miserable. >> report