The Northwestern University professor wanted in the fatal stabbing of a Chicago man has sent a video message to friends and family members apologizing for his role in the killing, police said Friday.

The new revelation came as Chicago Police spokesman Anthony Guglielmi said the hunt for noted microbiologist Wyndham Lathem and University of Oxford employee Andrew Warren has "intensified and narrowed" and investigators think they know where the men are or where they're going.

Investigators told Fox 32 that Lathem apologized in the video, but did not disclose exactly what he said, citing the ongoing investigation. Authorities did say that Lathem did not mention suicide in the message.

Lathem and Warren are wanted on first-degree murder charges in last week's killing of 26-year-old Trenton Cornell-Duranleau.

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. She declined to say whether she or other family members had ever heard of them before her son was killed because they "are at large and there's an ongoing investigation."

Cornell also issued the following statement to the AP: "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. We are asking that you allow our family to process and grieve this tragedy privately. We are asking all media outlets to not contact our family, friends or associates. When we have had sufficient time to mourn our child's passing, we will release a more in depth statement if we believe it is appropriate to do so."

Another Chicago police spokesman, Frank Giancamilli, characterized the June 27 attack at Lathem's apartment as "domestic in nature," but authorities would not discuss the possible motive in further detail. The attack was so violent that the blade of the knife believed to have been used to kill Cornell-Duranleau was broken, Guglielmi said.

Investigators are trying to determine how the men knew one another. They wouldn't say if they believe Warren and Lathem knew each other before Warren traveled to Chicago from England. Lathem and Cornell-Duranleau did cross paths, at least electronically: They are Facebook friends.

Lathem, a 42-year-old associate professor at Northwestern, has been a much sought-after speaker on pneumonic and bubonic plague and has been published in top scientific journals.

"He's been very competitive in terms of getting NIH (National Institutes of Health) funding for his work ... and is respected for high quality research,' said Bill Goldman, a professor and chair of microbiology and immunology at the University of North Carolina in Chapel Hill. Goldman has known Lathem since Lathem worked in his laboratory at Washington University before Lathem left for Northwestern in 2007.

Warren, who is British, is in charge of pensions and payroll at the University of Oxford's Somerville College, though his name and photograph have been removed from the school's online directory.

Cornell-Duranleau moved to Chicago from the Grand Rapids, Mich., area after he received his cosmetology license and worked as a hair stylist. It is unclear from his Facebook page where he was working at the time of his death.

Timber Baun-Crooks, the mayor pro-tem of Trenton, Mich., who gave Cornell-Duranleau a job at a hair salon four years ago, described him as a "great kid." But she said, "he wanted to be something so bad, though I don't know what that was or if he ever found his niche in life."