CHICAGO – DNA on a cigarette butt found after the killings of a federal judge’s mother and husband matches the Chicago electrician who killed himself during a traffic stop and claimed responsibility for the slayings in a suicide note, authorities said last night.

Chicago police spokesman Matthew Jackson said the state police crime lab confirmed the link to Bart Ross, who had filed bizarre, rambling lawsuits over his cancer treatment – including one dismissed by U.S. District Judge Joan Lefkow.

Police Superintendent Phillip Cline said that in addition to the suicide note, Ross, 57, also fit a witness description of a man seen leaving Judge Lefkow’s home the day of the killings.

“The DNA match, with all the other evidence, certainly convinces us that Ross is the offender in the Lefkow family homicide,” said another Chicago police spokesman, David Bayless. He stopped short of saying the investigation was closed.

Ross, 57, committed suicide Wednesday outside Milwaukee in West Allis, Wis., after police pulled him over because of broken taillights on his van.

Mr. Cline would not speculate on what Ross was doing in the area. But at least one other judge who ruled against him lived there. And a source close to the investigation told the Associated Press on condition of anonymity that the suicide note, found in Ross’s van, contained the names of judges.

Judge Lefkow came home February 28 to find her 64-year-old husband, Michael Lefkow, and 89-year-old mother, Donna Humphrey, shot to death in the basement.

Investigators had earlier suspected the slayings may have been the work of white supremacists angry over another of Judge Lefkow’s rulings. But Ross had no known connections to extremist groups.

Last fall, the judge had dismissed a lawsuit in which Ross accused doctors of disfiguring him when they treated him for cancer in the early 1990s. Among other things, he claimed doctors committed a “terrorist act” by giving him radiation without his consent.