CHICAGO >> A British man who admitted helping a former Northwestern professor fatally stab the professor’s boyfriend was sentenced Wednesday to 45 years in prison under a plea bargain.

Andrew Warren, 61, pleaded guilty to first-degree murder after agreeing to testify against co-defendant Wyndham Lathem as part of his 2019 deal, the Chicago Tribune reported. Cook County prosecutors agreed to recommend a prison term of 45 years.

Warren testified last year that he was an active participant in the slaying of Trenton Cornell. He said he hit Cornell over the head with a lamp and stabbed him twice.

Lathem was convicted of first-degree murder in October and sentenced last month to 53 years in prison.

Warren apologized to Cornell’s family in court..

“I just want to say that I’m really so sorry,” he said. “That’s all I can say.”

Prosecutors said Lathem and Warren made a pact to kill each other but instead killed Cornell, who was stabbed dozens of times and left in Lathem’s apartment.

Warren testified at Lathem’s trial that he met Lathem online and they made plans for him to travel to Chicago as part of a suicide plot, but instead they stabbed Cornell and fled town.

Cornell’s mother, Charlotte Cornell said a statement Wednesday that “instead of ending his (own) life, he ended a person’s life who he didn’t even know.” After the hearing, she said she agreed with Warren’s sentence and appreciated that he had come forward “to tell the truth.”

Under the plea agreement, prosecutors won’t oppose Warren applying to the U.S. Department of Justice’s International Prisoner Transfer Program, which can allow inmates to move to prisons outside the U.S. A transfer to a British prison could allow Warren to serve only about half his prison term.