Richard Allen is charged with killing Abby Williams and Libby German on an Indiana trail in 2017.
In court, prosecutors played an enhanced and extended video that Libby recorded on her phone the day she was killed. Jurors heard a phone call Allen made to his wife in which he confessed to the crime.
Defense attorneys told jurors that the investigation was botched.
Richard Allen pleaded not guilty to the murders of best friends Abby Williams, 13, and Libby German, 14. Their bodies were left in the woods on Feb. 13, 2017, and discovered the next day.
The crime gained national attention when police released an image of the suspect and a clip of his voice -- a recording of him saying "down the hill" -- which was recovered from Libby's phone.
Allen admitted to being on the trail the day of the murders but denied involvement.