NORRISTOWN, PA -- An Ivy League professor was charged Monday with bludgeoning his estranged wife to death as she wrapped presents a few days before Christmas.

Rafael Robb, 56, surrendered to authorities to face murder charges and was being held without bail.

A tenured economics professor at the University of Pennsylvania, Robb had told investigators he was in Philadelphia when his wife Ellen Robb was killed Dec. 22.

But prosecutors say his alibi didn't hold up and he had reason to kill his wife.

"Dr. Robb lied to the police about an obvious motive for this murder, his knowledge of his wife's recent plans to divorce him and obtain a significant portion of his wealth," according to a police affidavit. Ellen Robb, 49, had told family members she had hired a divorce attorney and was expecting $4,000 a month in support when she moved out Jan. 1, court papers said.

Robb's attorney, Francis Genovese, said he was surprised that the arrest warrant was largely based on circumstantial evidence.

"I was expecting I would see more hard evidence -- maybe forensic evidence -- come before pointing to Dr. Robb as the killer," Genovese said before his client's arraignment.

Robb was charged with first- and third-degree murder as well as evidence tampering, lying to authorities and a weapons charge.

Authorities say the murder scene at the couple's home in Upper Merion Township was staged to look like a burglary, but Ellen Robb's face was beaten so badly that her killer must have hated her.

A murder weapon has not been found but investigators believe it was a narrow metal object, such as a crowbar or a tire iron.

Prosecutors also question Robb's self-described actions after finding the body. Robb told police he touched his wife's body, brought his briefcase and laptop upstairs, checked on the family dog, stopped in the bathroom and laundry room, and then walked to his car before calling for help from a cell phone, according to the police affidavit.

Robb dialed the local 10-digit number for police rather than calling 911, officials said.

"We think he erroneously thought the regular police number wasn't taped," District Attorney Bruce Castor said Monday.

"Her head is cracked," Robb told a police dispatcher, indicating that he believed Ellen Robb was beaten. But authorities said her injuries were so extensive they initially thought she was killed with a shotgun blast to the face.

Castor also suggested that Rafael Robb went out of his way to get a parking ticket in the city and appear on a store security tape to support his alibi. But they say he lied about spending some 40 minutes at a Chinatown grocery buying fruit. The clerk told police she knew him but did not see him that day, authorities say.

Rafael Robb denied any involvement in the slaying last week when questioned by a reporter and declined to comment outside the courthouse Monday.

He and Ellen Robb had been married since 1990 but had kept separate bedrooms in recent years. Ellen Robb was described as a stay-at-home mother who doted on their only child.

Robb, a native of Israel, has been at Penn for at least four years, according to a resume posted on his university Web site.

University officials said only that that someone else would be teaching Robb's graduate seminar in game theory this semester. Game theory involves the use of strategy to bring about the most favorable outcome in a given situation.

(Copyright 2007 by The Associated Press. All Rights Reserved.)