The digital forensics team who worked on the Bryan Kohberger case tells PEOPLE that he spent over three hours on the phone with his mother after killing four University of Idaho college students

Kohberger, 30, called his mother, Maryann Kohberger, at 6:17 a.m. on Nov. 13, 2022, when arriving at his Washington State University campus home after the quadruple killing.

Bryan Kohberger immersed himself in serial killer case files as a PhD student at Washington State University prior to the brutal quadruple Idaho murders that landed him behind bars for the rest of his life.