Updated

A former Ivy League professor pleaded guilty Monday to manslaughter for killing his wife as she wrapped Christmas presents last year, telling a judge he "just lost it" during an argument.

Rafael Robb, once a tenured economics professor at the University of Pennsylvania, faces a likely prison sentence of 4 1/2 to seven years for bludgeoning his wife, Ellen, on Dec. 22.

Robb, 57, said Monday that he got into an argument with his wife about a trip she was taking with their daughter and whether they would be returning in time for the daughter to return to school.

"We started a discussion about that. The discussion was tense," Robb said. "We were both anxious about it. We both got angry. At one point, Ellen pushed me. ... I just lost it."

Ellen Robb, 49, was beaten to death in the kitchen of their home in Upper Merion Township, outside Philadelphia. Partly wrapped Christmas presents were nearby.

"It's a classic heat-of-passion killing," said Montgomery County District Attorney Bruce Castor, who offered Robb the chance to plea guilty to the manslaughter charge.

Robb's attorney and prosecutors say Robb feared his wife was leaving him and would keep him away from their daughter.

Detectives believed the scene had been staged to look like a burglary. The murder weapon — a chin-up bar that hadn't been installed yet, Castor said — was not found.

Robb was an expert in game theory, a complex melding of psychology, human behavior and economics — all aimed at determining what one's adversary will do next.

With that background, police say, Robb may have thought he could outsmart them.

He and Ellen Robb had been married since 1990 but had long been estranged — keeping separate bedrooms — while living together in the house.

Ellen Robb was described as a stay-at-home mother who doted on their only child.

Rafael Robb apologized to his 13-year-old daughter, Olivia, and family in court Monday.

"I know she liked her mother. ... And now she doesn't have a mother," he said, stifling tears.

Robb, who has been held without bail, spoke to his daughter by phone over the weekend and told her that he was responsible for the killing. They have not seen each other since he was arrested earlier this year.

Olivia Robb is being raised by Ellen Robb's brother Art Gregory in the Philadelphia suburb of Haddonfield, N.J.

Gregory and another brother, Gary Gregory, said after the proceeding Monday that their sister had been verbally abused by Rafael Robb during the marriage, but stayed with him because of their love for their daughter.

Rafael Robb, a native of Israel, earned a Ph.D. in economics from the University of California at Los Angeles, in 1981. He had been at Penn for at least four years when the slaying occurred.

Sentencing will likely take place in a few months. Guidelines call for a prison term of 4 1/2 to seven years, but Castor said the statute allows anything from probation to 10 to 20 years.