Three months ago, Montgomery County prosecutors were so optimistic that bloody footprints around a slain Main Line woman's body would implicate her college-professor husband that they carved out and removed that part of the floor for FBI experts to study.

But last week, Rafael Robb's attorneys argued in motions that the prints in fact could exonerate the University of Pennsylvania economics professor, whose size-12 shoes were much larger than those worn by Ellen Robb's killer.

The attorneys were set to plead the matter in Montgomery County Common Pleas Court yesterday, but results of the FBI tests weren't back yet. Judge Paul W. Tressler continued the case and set a May 7 trial date after Robb, through his attorneys, waived his formal arraignment and pleaded not guilty to murder and related charges in the Dec. 22, 2006, death of his wife. Robb did not attend the proceeding.

District Attorney Bruce L. Castor Jr. confirmed he would not seek the death penalty in the case, because authorities haven't identified any aggravating circumstances to elevate it to a capital case.

Castor acknowledged that the case probably wouldn't hinge on the prints, which were partial and didn't match any shoes Robb is known to own. Still, he noted that Robb admitted he'd recently discarded two pairs of work boots, preventing detectives from comparing the crime-scene prints to the missing boots.

Robb's attorneys, Frank DeSimone and Frank Genovese, declined to comment after yesterday's proceeding.

Ellen Robb, 49, who had a 12-year-old daughter with her husband, was ambushed and bludgeoned to death as she wrapped Christmas gifts in the kitchen of her Wayne home on the morning of Dec. 22.

Detectives decided that the crime scene had been staged to look like a burglary had occurred. They grew skeptical after deducing that glass from a busted rear window hadn't been stepped on or tracked throughout the house - as it would have been if an intruder had broken in.

Police never found the murder weapon, believed to be a pipe-like object.

They noted that a crowbar seen by relatives and visitors in recent years in the couple's garage was missing.

A forensic psychiatrist said the slaying - an "enraged blitz attack" - was a "crime between intimates," according to court records.

When Robb was arrested in January, Castor described the murder as having been motivated by the fury of a husband intent on ensuring that his divorce-minded wife wouldn't clean out his bank accounts. The couple had been estranged and lived separate lives for 10 years, though they resided in the same house. Ellen Robb had begun divorce proceedings a few weeks before her slaying.

But defense attorneys, in asking for the case to be thrown out, noted that the prosecution's evidence is wholly circumstantial with nothing directly tying Robb to his wife's slaying.

"The evidence in its totality was insufficient as to all charges," DeSimone wrote in a motion filed April 3. *