FBI and Chicago-area police are working around the clock investigating the case. A source tells The Associated Press that a shard of glass from a broken window at Lefkow's house has been sent to an FBI lab for analysis. The shard has what appears to be a fingerprint.
Lefkow told a newspaper Wednesday she fears the murders of her husband and mother may have been related to her job, saying she is furious over what she called a "cold-blooded" attack.
"If someone was angry at me, they should go after me. It's not fair to go after my family," Lefkow said in an interview posted on the Web site of the Chicago Sun-Times on Wednesday night. "It was just cold-blooded. Who would do this? I'm just furious."
Lefkow's remarks came as two of her colleagues called for greater security for federal judges and their families following the execution-style murders of her husband, Michael, and her 89-year-old mother, Donna Humphrey.
A promising-but-narrow set of evidence is being pieced together, reports CBS News Correspondent Cynthia Bowers. Among the most promising in a number of leads are a partial handprint, a bloody shoe print, as well as a witness report of two men with military-style haircuts seen sitting in a car parked near the Lefkow home.
Investigators describe one man as white in his mid 20's, between 5'8" and 6 feet tall, with strawberry blonde hair and medium build. They say he was seen in a vehicle at the north end of Judge Lefkow's block Monday morning.
Police say the second man is also white, 50 to 60 years old, 5'10" to 6 feet tall. They say he has hazel eyes, large build and was last seen wearing dark green coveralls, a black skullcap and grayish-green coat.
Investigators are hoping that an abundance of physical evidence left behind in the basement where the victims were killed will point to specific suspects.
"This horrible tragedy has got to serve as the basis for a substantial increase in security for judges and their families," U.S. District Judge Wayne R. Andersen said. "The Internet is plastered with information about every one of us."
The shooting came a month before white supremacist Matthew Hale was to be sentenced by another judge for soliciting an undercover FBI informant to murder Lefkow, who had ordered Hale to change the name of his extremist group as part of a trademark lawsuit.
Police say extremist groups are just one of several avenues being looked at by authorities, though speculation among judges and lawyers has focused on Hale's group, which has a history of violence.
Both victims had been shot multiple times, according to the Cook County Medical Examiner's office, and a source told the AP that police found two .22 caliber casings at the scene. Investigators believe the victims were forced to lie on the basement floor before being shot, the Chicago Tribune reported Wednesday, citing unnamed sources.
A federal source who spoke on condition of anonymity said a shard of broken glass from a broken window in the Lefkow home contained a fingerprint and was flown to Washington for examination. The source said police also were analyzing a bloody footprint left at the home.
Authorities were looking into the source of several phone calls Lefkow and her family received Sunday night that might have come from a correctional facility, the Chicago Sun-Times reported Wednesday, citing a police report.
As recently as last year, federal authorities took the murder plot that Hale hatched seriously enough that they provided protection for Lefkow for at least a few weeks and Chicago police stepped up patrols of her neighborhood. The Lefkows also took their own security measures, installing cameras on their front porch, said Mike Miner, a senior editor at the Chicago Reader and longtime friend of the couple.
Hale's father, retired East Peoria policeman Russell Hale, dismissed the notion that his son was involved in the slayings, saying he is under constant surveillance at the federal correctional center in Chicago and the FBI closely monitors his phone calls and visits with family members.
"There would be no way he could order anything," said Hale. "It's ridiculous."
Nonetheless, white supremacists seem to be following the case closely. As Bowers reports, in the chat rooms of white supremacist web sites, talk of the murders has ranged from celebration to concern about a crackdown.
Currently, Hale, the self-proclaimed "Pontifex Maximus" of the World Church of the Creator, sits in a cell, isolated from other inmates and allowed only rare visits from his parents. But investigators want to know whether his malign influence extended beyond the prison walls.
Police said the possibility that the slayings were committed by hate groups was "but one facet of our investigation" and cautioned against jumping to that conclusion.
Lefkow was nominated to the U.S. District Court bench by President Clinton in 2000. She has sentenced defendants in the political corruption case involving former Gov. George Ryan, decided the mental fitness of a man suspected of shooting a police officer and ordered the makers of Beanie Babies to pay $700,000 in a trademark case.
Friends of the Lefkows were stunned that anyone would want to harm Michael Lefkow, an attorney, who with his wife was active in the Episcopal Church.
"He was a delightful person," said Eleanor Lukens, one of about 30 people who gathered Tuesday night at the family's church, St. Luke's in Evanston. "This is a terrible tragedy, a shock to the entire congregation."
Lefkow said she never thought her job would endanger her family.
"I think we all sort of go into this thinking it's a possibility, but you don't think it's going to happen to you because it's so unthinkable," she told the Chicago Tribune.