By MARYCLAIRE DALE
Associated Press

NORRISTOWN, Pa. - A former Ivy League professor pleaded guilty Monday to voluntary 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-and-a-half 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, described as a stay-at-home mother who doted on their only child, died in the kitchen of their home in Upper Merion Township, outside Philadelphia.

"It's a classic heat-of-passion killing," said Montgomery County District Attorney Bruce Castor.

Robb's attorney and prosecutors say Robb feared that 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, described by Castor as a chin-up bar, was not found.

The couple married in 1990 but had long been estranged, keeping separate bedrooms.

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 during the weekend and told her he was responsible for the killing. They have not seen each other since his arrest. Olivia is being raised by a brother of Ellen Robb.

Sentencing will likely take place in a few months. Guidelines call for a term of 4-and-a-half to seven years, but Castor said state law allows anything from probation to 10 to 20 years.