A DNA match from a cigarette butt convinced police that a Chicago electrician was the killer of a federal judge's husband and mother, authorities said.

The cigarette butt found in Judge Joan Humphrey Lefkow's (search) house was matched to the electrician, Bart Ross (search), who killed himself during a traffic stop in Wisconsin this week, and the evidence points to him as the lone killer, police spokesman David Bayless said.

Ross, whose rambling lawsuit over his cancer treatment was dismissed by Lefkow, had claimed responsibility for the killings in a suicide note found in his minivan.

"The DNA match, with all the other evidence, certainly convinces us that Ross is the offender in the Lefkow family homicide," Bayless said Thursday night.

The judge had returned home from work on Feb. 28 to find her husband and 89-year-old mother fatally shot in the basement. She described Ross as "a very pathetic, tragic person," in an interview with The New York Times published in Friday's editions.

"I guess on one level I'm relieved that it didn't have anything to do with the white supremacy movement, because I feel my children are going to be safer," the judge said. "It's heartbreaking that my husband and mother had to die over something like this."

The judge and her daughters have been in protective custody since the slayings.

Authorities initially focused on associates of white supremacist Matt Hale, who was convicted last year of soliciting Judge Lefkow's murder. But a letter found Wednesday night after Ross's suicide instead tied him to the killings, police Superintendent Phil Cline said.

Hale's father, Russell, said he felt terrible for the Lefkow family but "great relief" for his own family when he learned of Ross' link to the slayings.

Lefkow last fall dismissed a rambling lawsuit in which Ross claimed that cancer treatments had disfigured his face and that the U.S. judicial system, which dismissed his medical malpractice claims, "is the Nazi style criminal and violator" of his civil rights. Lefkow's ruling was upheld by a federal appeals court in January.

Ross, a 57-year-old Polish immigrant with no known ties to extremist groups, shot himself to death on a suburban Milwaukee street after an officer pulled him over for broken brake lights.

"We came upon a note, written presumably by the victim, where he implicated himself in the murders of Michael Lefkow and Donna Humphrey," Cline said. "In the note, the offender outlined in some detail the events of Monday, February 28th."

"We're satisfied that there's information in the letter that would point us to Ross being in Lefkow's house," he said.

Besides the suicide note, police were reviewing a handwritten letter received by WMAQ-TV on Thursday and signed by a Bart Ross; the writer described breaking into the Lefkow home before dawn on Feb. 28 with a plan to kill the judge.

The letter said he killed Lefkow's husband and mother around 9 a.m. after they discovered him hiding in the basement.

"After I shot husband and mother of Judge Lefkow, I had a lot of time to think about life and death. Killing is no fun, even though I knew I was already dead. I gave up further killings on about 1:15 p.m. on Feb. 28, 2005, and left Judge Lefkow's house," the station quoted the letter as saying.

Neighbors said Ross, who changed his name from Bartlomiej Ciszewski after he emigrated from Poland in 1982, lived alone with his dog and kept to himself. They described him as intelligent but increasingly angry as his legal fight over his treatment for mouth cancer repeatedly failed.

After Ross's suicide, federal marshals also began calling judges named in a letter found in his van.

Authorities said they didn't know why Ross was in the Milwaukee area on Wednesday. Two federal appeals court judges who upheld dismissals of his lawsuits have offices in Milwaukee. One of those, Terence Evans, said marshals called at 3 a.m. to inform him of the situation. A person answering the phone for the other judge, John Coffey, said he would have no comment.

"As any federal judge who may be involved in a decision, we have concerns, and we took those concerns seriously and acted upon them," said U.S. Marshal William Kruziki.

Ross' vehicle was issued a $20 parking ticket in downtown Milwaukee Wednesday afternoon about four blocks from the federal courthouse, where Evans and Coffey have offices, said Cecilia Gilbert of the City of Milwaukee Department of Public Works.

Around the same time, courthouse security saw Ross walking around the building, the Chicago Sun-Times reported, citing unidentified sources.

Federal Judge David H. Coar, who also dismissed a Ross lawsuit, was working out in a gym at 6 a.m. when his wife called to say the marshals had telephoned with the news.

"I don't think security is adequate and I never have thought security is adequate," Coar said. Two other federal judges in Chicago said the same in the wake of the shootings.

In the lawsuit Lefkow dismissed, Ross said his cancer treatments had disfigured his face and caused his teeth to fall out. He accused four doctors of committing "a terrorist act" in giving him radiation therapy.

Ross compared his radiation and surgery with the experiments Nazi doctors performed in concentration camps, demanded the impeachment of judges who had ruled against him, and asked for $250 million in damages from the federal government.

"As his legal remedies were becoming fewer, as he had less success, he became more angry, more agitated," said lawyer Thomas Browne, who represented an attorney Ross was suing.

More setbacks came in the last two months as the 7th U.S. Circuit Court of Appeals affirmed Lefkow's decision to dismiss his latest lawsuit and his landlady began proceedings to evict him from the home he once owned.

A hearing in the eviction case had been scheduled for Thursday.