How Police Actually Cracked the Idaho Killings Case

Around 4 a.m. on Nov. 13, a masked man broke into a house about a mile from the University of Idaho campus and stabbed four students. Then he walked past a stunned, surviving roommate and left. By the time police arrived, Kaylee Goncalves and Madison Mogen, two 21-year-old best friends, and Ethan Chapin and Xana Kernodle, two 20-year-olds who were dating, were dead.

Early on in the investigation, the Moscow Police Department became interested in a white Hyundai Elantra that surveillance footage had captured near the house that morning. Police compiled lists of white Hyundai Elantras, spanning from 2011 to 2016, that were registered at local universities and instructed officers to search for still more. An affidavit released last week revealed that on Nov. 29—just two weeks after the crime—these techniques succeeded in identifying a 2015 Elantra registered to Bryan Kohberger, a 28-year-old criminology student at nearby Washington State University.

And yet it would be another month before police arrested Kohberger and charged him with the murders. All the while, investigators would keep pleading for more tips about Elantras. That’s because...