Bryan Kohberger was on the phone with his mom less than two hours after killing four University of Idaho students and investigators say the timing shreds his alibi.

Digital forensics expert Heather Barnhart told PEOPLE, Kohberger called his mom at 6:17 AM on November 13, 2022 — shortly after getting back to his Washington State University apartment after carrying out the gruesome murders of Madison Mogen, Kaylee Goncalves, Xana Kernodle and Ethan Chapin.

According to Barnhart, he tried calling his mom at 6:13 AM, then called his dad when she didn’t pick up. Kohberger and his mom talked for 36 minutes, and at 8:03 AM, Kohberger rang her again for 54 minutes right around when prosecutors say he drove back toward the crime scene.

Minutes after leaving, at 9:00 AM, he was back on the phone with her for 9 minutes. By the end of the day, mother and son had clocked more than 3 hours of calls. Barnhart’s team also discovered Kohberger’s cell phone was shut off from 2:54 to 4:48 AM with a fully charged battery during the murders.