Joseph "the Clown" Lombardo was at a workbench in his small Near West Side shop, where masonry saws and tools are sharpened, when 10 federal agents swarmed in.

One agent waved a grand jury warrant, another carried a cotton swab. The agents dabbed the inside of Lombardo's mouth with the swab--gathering DNA--and were gone in less than two minutes.

Lombardo, a longtime Chicago Outfit leader who publicly swore off his mob ties after being released from prison in 1992, is one of more than a dozen mob bosses and associates who are subjects of a new federal probe into long-dormant mob murders, some dating as far back as three decades.

A federal grand jury is investigating at least 16 unsolved killings, making it one of the biggest law-enforcement strikes against organized crime in Chicago history. Sources close to the investigation--dubbed Operation Family Secrets--and attorneys for some of the alleged mob members say they expect the grand jury to hand up indictments as early as next month.

Convictions on this scale would be unprecedented. The Chicago Crime Commission counts 1,111 Chicago-area gangland slayings since 1919, but only 14 have ended in murder convictions and three cases were cleared when the suspected killers were murdered before being arrested, according to the commission. The crime commission is a non-profit group of civic leaders that aim to improve public safety.

Prosecutors not only have new DNA technology drawing out evidence from old cases but also have cooperating witnesses, including at least one member of the notorious 26th Street Crew, sources said. Nick Calabrese, a high-ranking crew member, spent years in a Michigan federal prison before turning informant and fingering past associates in several murders, according to sources.

Working on the tips, federal investigators have fanned out across the Chicago area, swabbing more than 30 known Outfit associates for DNA samples to try to link them to some of the area's most notorious gangland slayings.

Like the 1974 murder of Daniel Seifert. Scheduled to testify against Lombardo and other Outfit members in a Teamsters pension loan fraud case, Seifert was slain by shotgun blasts by ski-masked men outside his Bensenville plastics factory as his wife and 4-year-old son watched.

Federal prosecutors hope DNA from a hair strand lifted from one of the ski masks found under a getaway car in that case could link Lombardo to the crime scene.

Though the investigation has focused heavily on the 26th Street Crew, investigators have tossed a wide net, hoping to snare members of different crews in cases ranging from the 1970 disappearance of Michael Frank "Bones" Albergo, a 220-pound organized crime muscleman, to the 1986 murder of Anthony Spilotro, the Outfit's man in Las Vegas who fell out of favor with his bosses. He and his brother, Michael, were beaten and buried in an Indiana cornfield. Dust and sand found in their lungs indicated they had been buried alive, officials said.

Top mob bosses probed

Besides Lombardo, other mob associates that agents are investigating include John "No Nose" DiFronzo and Jimmy Marcello, considered two of the Outfit's top-ranking bosses, a source familiar with the investigation said.

"It's a pretty massive investigation from the stuff I'm hearing," said Rick Halprin, Lombardo's attorney. Halprin said Lombardo, now 75, was at a Chicago police station reporting a stolen wallet at the time of the Seifert murder.

Albergo, an alleged loan shark for the mob, was scheduled to stand trial on charges of criminal usury and conspiracy when he disappeared in September 1970. Authorities at the time speculated he may have been killed for not realizing he was making illegal loans to an undercover Chicago policeman.

In 2003, Albergo's name resurfaced when FBI agents excavated an edge of the parking lot at U.S. Cellular Field, reportedly looking for his bones, sources said. Calabrese led authorities to the site, the sources said.

Two other murders expected on the indictment are those of William and Charlotte Dauber, who were gunned down by rifle and shotgun blasts in a car chase on a rural Will County road in 1980. The couple's bodies were found sprawled across the front seat of their Oldsmobile, with three of its windows blown out and its front end crushed against a tree.

William Dauber, a reputed Outfit hit man who authorities believed was responsible for more than 30 slayings, had been arrested on federal drug charges and mob leaders feared he would turn informant.

One of the more notorious slayings expected on the indictment is that of Anthony Spilotro.

The Outfit's enforcer in Las Vegas, Spilotro had angered his bosses by indulging in a series of burglaries, dope deals and murders that brought unwanted federal attention.