A bubonic plague expert and an Oxford University administrator are under arrest after allegedly slaying a young Chicago hairstylist and fleeing halfway across the country.

On the night of July 27, Chicago police received a phone call from a desk clerk at a luxury apartment building in the city’s River North neighborhood. The clerk had received a call of his own, warning him of a crime in one of the apartments, he said. When police arrived on the scene, they found Trenton Cornell-Duranleau, a 26-year-old hair stylist, dead of multiple stab wounds.

The apartment’s owner, Northwestern University professor Wyndham Lathem, was last seen that night leaving the building with Oxford University employee Andrew Warren. Both men went missing for over a week before they were arrested separately in California on Friday: Lathem in Oakland, and Warren in San Francisco.

Before the murder, Cornell-Duranleau and the 42-year-old Lathem may have been romantically involved, according to The Chicago Tribune. Chicago Police spokesperson Anthony Guglielmi told the Tribune that the pair had an unspecified relationship, but had “some type of falling out.” Sources told the paper that Lathem and Cornell-Duranleau were allegedly dating.

Cornell-Duranleau’s friends described him as a free-spirited young man who loved to make people laugh, and who sometimes dated men closer to Lathem’s age.

“He was always an upbeat person,” Cornell-Duranleau’s former co-worker Julie Donaldson told The Daily Beast. “I knew him when I was going through beauty school with him. He was a mentor, he taught me a lot.”

Cornell-Duranleau was “a clean cut guy. Never involved in drugs, never smoked, we invited him out to drink one time and he declined,” Donaldson said. She added that Cornell-Duranleau was dating an older man at the time, and had recently moved away to Chicago.

“I don't know why he did move to Chicago,” former co-worker Sheena Franzel-Wils said. “I remember he moved to Missouri, I think a few years ago, and then things didn't work out and he moved back to Michigan for a while.”

Franzel-Wils said Cornell-Duranleau sometimes dated men closer to Lathem and Warren’s ages, a fact that Cornell-Duranleau also advertised on his profile on a dating site that connects younger people with older partners. Though Cornell-Duranleau’s relation to Lathem and Warren is unclear, police are reportedly investigating domestic violence as a motive.

Lathem’s name is usually associated with ancient deaths. The Northwestern University professor studies microbiology and immunology, with a particular focus on the bubonic plague. The work led him to study DNA samples from medieval grave sites.

"We want to see if it's gotten more or less deadly over time," Lathem told the Chicago Reader while studying a particular plague strain in 2013.

The scene in his apartment last Thursday was a deadly one indeed. The ritzy pad was covered in blood, police sources told the Chicago Tribune. A knife with a snapped blade lay in the kitchen trash can. Another knife sat next to the sink.

And in the bedroom, Cornell-Duranleau was lying face down, dead of multiple stabs to the back.

Shortly before police arrived on the scene, security cameras spotted Lathem leaving the apartment with Andrew Warren, a 56-year-old treasurer at Somerville College, a school within Oxford University. Warren lived in the U.K., and had only recently come to the U.S., Chicago PD’s Guglielmi told the Associated Press. (Lathem appeared to be planning a move to Europe. Near the end of the Northwestern school year, he tweeted that he was leaving the university, and employees at a Paris-based laboratory tweeted to welcome him to their team.)

But while cops were investigating the crime scene, one of the alleged killers was at a Wisconsin library making a $1,000 cash donation in Cornell-Duranleau’s name, police say. The man, whom police have not named, reportedly entered a library in Lake Geneva, Wisconsin, a few hours’s drive from Chicago, and gave a desk clerk $1,000 as a “general donation” under Cornell-Duranleau’s name.

Lathem also allegedly sent a video message to family and friends apologizing for “his involvement” in the murder, which he called the “biggest mistake of his life,” Guglielmi said Friday.

While police have yet to announce a motive for the slaying, their investigation appears to point to the relationship between Lathem and his alleged victim. After the killing, managers at Lathem’s apartment building sent residents an email informing them that Chicago Police were investigating “a variety of motives, including a possible domestic incident,” the Chicago Sun-Times reported.

When Lathem and Warren surrendered to law enforcement in California on Friday, the two men appeared tired and disheveled from their week on the run. They are being held in California, where investigators are beginning the long process of discovering what happened in Lathem’s apartment on July 27.

“We hope today’s arrest brings some small level of closure and justice” for Cornell-Duranleau’s family, Chicago police said Friday.