For more than a week, the gruesome killing of a young hairstylist in a downtown Chicago luxury high-rise has captivated the region, the case’s surprising twists mystifying even the detectives who eventually tracked down two suspects.

It started with an anonymous phone call late on July 27 to the front desk of the Grand Plaza, a 57-story apartment building near the Chicago River. There had been a crime committed on the 10th floor, the caller said.

The police soon entered Unit 1004 to find blood nearly everywhere and the body of Trenton Cornell-Duranleau, 26, who had been stabbed so violently that the blade broke off the knife used in the attack, the authorities said. Missing were the apartment’s owner, Wyndham Lathem, an associate professor at Northwestern University, and a British man seen on the building’s surveillance cameras with him, Andrew Warren.

Over the next week, detectives with the Chicago Police Department cast a wide net, eventually involving federal authorities and British law enforcement officials as they tracked the two men’s movements across the western half of the United States. Along the way, developments in the case — a donation in the victim’s name at a Wisconsin library and a remorseful video recorded by Mr. Lathem — puzzled investigators and added to their urgency.