Transcript for Suspect describes killing childhood friend in alleged confession tape
video of a murder trial in new Jersey. Prosecutors playing the video and what they say it proves. Here's erielle reshef. Reporter: Tonight, those chilling tapes of what New Jersey prosecutors say is a clear confession by an accused killer. It took me half an hour to kill her. Reporter: The recordings appearing to show Liam mcatasney coldly describing how he murdered 19-year-old Sarah stern in December 2016,both 16 years old at the time. I choked her out, drag her. And my biggest problem was the dog and her dog laid there and watched as I killed her. Didn't do anything. Reporter: The motive prosecutors say to steal cash from stern. The worst part of it is I thought I was walking out 50 grand to 100 grand in my pocket. She had one safe that she took money out, and she only had 10 grand." Reporter: That secretly recorded video part of a sting operation using mcatasney's Frie Anthony curry. His defense arguing he fabricated the story for a horror film that curry was working on. Mcatasney is plead not guilty, denying any wrongdoing and faces life in prison without parole if convicted. David? Thank you.
This transcript has been automatically generated and may not be 100% accurate.