Investigators are closing in on a Northwestern University professor and University of Oxford staffer who are wanted in the fatal stabbing in a River North apartment, a police spokesman said Thursday.

The hunt for Wyndham Lathem and Andrew Warren has “intensified and narrowed,” with the U.S. Marshals Service and law enforcement agencies across the country joining in the manhunt, Chicago Police spokesman Anthony Guglielmi said on Thursday, four days since a Cook County judge issued an arrest warrant for the pair.

“The search for them will only intensify,” Guglielmi said. “They should do the right thing and turn themselves in to any police station. It’s only a matter of time.”

Lathem, a respected microbiologist at Northwestern’s Feinberg School of Medicine, and Warren, who was visiting Chicago from England, are wanted on first-degree murder charges in last week’s killing of 26-year-old Trenton Cornell-Duranleau.

Lathem, who shared an apartment with Cornell-Duranleau in the luxe Grand Plaza apartments, had been a suspect since police first were tipped to the murder by a cryptic phone call to the front desk of the building on July 27.

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Guglielmi said the night Cornell-Duranleau was killed, an attendant working the front desk received  the call in which a male caller said, “There may have been a crime committed in Room 1004. You need to check it out.”

The attendant called the room, and when he got no response, called police. Officers entered the apartment with the building manager, and discovered a “gruesome scene,” Guglielmi said. Cornell-Duranleau had been stabbed multiple times, according to the Cook County medical examiner, and Guglielmi said the blows landed with such force that the knife believed to be the murder weapon snapped.

Guglielmi said Cornell-Duranleau and Lathem had a “domestic relationship,” but did not know how the two men were connected to 56-year-old Warren, who managed payroll and pensions for Oxford College’s Sommerville College in England.

Cornell-Duranleau’s mother, Charlotte Cornell, told The Associated Press by phone from Michigan, where her son grew up, that the family doesn’t know the suspects.

“Our Family is deeply saddened by the death of our son. It is our hope that the person or persons responsible for his death are brought to justice,” Cornell said in a statement given to the AP.  Cornell-Duranleau’s funeral is set for next week in his hometown of Lennon, Michigan.

Lathem, a 42-year-old associate professor at Northwestern, has been a sought-after speaker on pneumonic and bubonic plague and has been published in top scientific journals, said Bill Goldman, a professor and chair of microbiology and immunology at the University of North Carolina in Chapel Hill. Lathem has worked at Northwestern since 2007.

Cornell-Duranleau moved to Chicago from the Grand Rapids, Michigan, area after he received his cosmetology license and worked as a hair stylist.

Timber Baun-Crooks, the mayor pro-tem of Trenton, Michigan, once gave Cornell-Duranleau a job at a hair salon. She described him as a “great kid.”

“He wanted to be something so bad,” she said. “Though I don’t know what that was or if he ever found his niche in life.”

Contributing: AP