As the week-long search for a Northwestern University professor suspected in a gruesome River North stabbing continued Friday, twists added to a murder story that has captivated a city that has seen more than 400 killings already this year.

Police revealed that fugitive microbiologist Wyndham Lathem had sent an apologetic video message to his friends, family and relatives of Trenton Cornell-Duranleau, the 26-year-old hair stylist he and an Oxford University employee are suspected of killing inside Lathem’s State Street high-rise last week.

CPD spokesman Anthony Guglielmi declined to comment on what Lathem said in the video, though CNN reported Lathem confessed to committing “the biggest mistake of my life,” and said the message had been encrypted.

On Friday, Guglielmi said the U.S. Marshals Service had taken the lead in the manhunt, and urged the two fugitives to turn themselves in, and referred anyone who has seen them to send information to the department’s anonymous tip webpage,

“We don’t want to see Professor Lathem harm himself, or anyone else. We don’t want this tragedy to get worse,” he said. “We want to facilitate a safe surrender.”

Lathem, a leading expert on the pathogens that cause the plague who had been on the Northwestern faculty since 2007, has not been seen since Cornell-Duranleau’s body was discovered in Lathem’s 10th-floor apartment on July 27.

Trenton H. James Cornell-Duranleau

A Cook County judge on Monday issued an arrest warrant for Lathem and Andrew Warren, a 56-year-old pension and payroll officer at a branch of Oxford University in England.

Police said that Cornell-Duranleau had been stabbed multiple times, leaving the apartment a “gruesome scene.”

Sources told The Chicago Sun-Times’ Michael Sneed that Cornell-Duranleau’s genitals were mutilated, and that fatal attack was so violent, the knife believed to be the murder weapon broke.

Stranger still, after fleeing the apartment, Lathem, 42, and Warren apparently traveled to Lake Geneva, Wis., and made a $1,000 donation to the public library in Cornell-Duranleau’s name.

The connections between the three men remain unclear. Lathem and Cornell-Duranleau lived together in the luxe condo, just blocks from tourist destinations like the Rainforest Cafe, and about a mile from Lathem’s lab at Northwestern’s Feinberg School of Medicine.

Colleagues described Lathem as a brilliant researcher who made important discoveries about the pathogens that caused the pneumonic plague, but who seldom discussed his personal life around the lab.

London’s Sun newspaper on Friday detailed screenshots of Warren’s profile on the Grindr dating app, which the tabloid said showed Warren saying he was seeking a dominant person, and that he had “no limits.” Warren’s family had reported him missing three days before Cornell-Duranleau’s body was discovered by police, the London Telegraph reported, and Warren left behind a boyfriend to make his first trip to the U.S.

Cornell-Duranleau had moved frequently after arriving in Chicago from his small hometown in Michigan a few years ago, friends said. Even in Michigan, he bounced among jobs after finishing his cosmetology degree.

Authorities said they have some idea of where the two fugitives might be.

Warren and Lathem’s passports were flagged, likely barring them from leaving the country.