Senior U.S. District Judge Edward F. Harrington, who was Boston's U.S. attorney during the Carter administration, said ex-agent John Connolly's contributions were "without parallel" in prosecutions that weakened the powerful Patriarca family. That included planting a listening device at the family's Boston headquarters.

"John Connolly had great ability and he had a certain flair that attracted a confidence and trust of underworld figures," said Harrington, the leadoff witness for Connolly's defense.

Connolly, 68, was the FBI handler of James "Whitey" Bulger and Stephen "The Rifleman" Flemmi, leaders of Boston's violent Winter Hill Gang and rivals of the larger Mafia.

Connolly faces life in prison if convicted of conspiracy and murder charges. Prosecutors accuse him of telling Bulger and Flemmi that gambling executive John Callahan might implicate them in an Oklahoma businessman's slaying.

Callahan, former president of World Jai-Alai, was found fatally shot in the trunk of his Cadillac at Miami International Airport in August 1982. Hit man James Martorano testified earlier in the trial that he killed Callahan based on Connolly's information.

Prosecutors rested their case last week after calling 19 witnesses, including several former Boston mobsters. Some testified that Connolly, who retired in 1990, tipped Bulger and Flemmi to an imminent 1995 indictment, allowing Bulger to evade arrest and remain a fugitive to this day.

Donald K. Stern, the Boston U.S. attorney from 1993 to 2001, also took the stand, suggesting that leaks about the Winter Hill investigation were a concern because they might tip the mobsters off.

"I had concerns that information presented to the grand jury was appearing in newspapers," Stern said.

Harrington, appointed to the federal bench in 1988, said he was involved in the fight against organized crime beginning in 1961 as a Justice Department prosecutor under then-Attorney General Robert F. Kennedy. Harrington said a top priority was recruiting criminals and others with direct access to the secretive Mafia hierarchy.

"It was through top echelon informants that they were able to penetrate the inner sanctum of this secret society," the judge said. "It's the business of crime on a daily basis, including murder."

FBI agents such as Connolly were sometimes "caught in the middle" between FBI guidelines requiring them to report crimes committed by top informants such as Bulger and Flemmi and the need to keep the information pipeline flowing, Harrington said.

During cross-examination, Prosecutor Michael Von Zamft focused on whether that meant criminal informants could commit crimes with impunity.

"That does not give them a license to commit murder, does it?" Von Zamft asked.

"It does not," Harrington replied.

Von Zamft also asked if it would be all right for Connolly to tell Bulger and Flemmi about others who might be cooperating with law enforcement, which would make them targets for assassination.

"The answer is no," Harrington said.

Harrington also said he had violated a judicial code of conduct rule by writing a letter on official stationery in support of Connolly to a judge presiding over the former agent's 2002 trial on racketeering and other charges. Connolly was convicted in that case and is serving a 10-year sentence.

The defense planned to call former FBI undercover agent Joseph Pistone, whose real-life penetration of the Mafia as "Donnie Brasco" was made into a 1997 movie. Pistone, however, asked to testify wearing sunglasses as a partial disguise, even though he has frequently been photographed and made TV appearances.

Prosecutors and news reporters objected. Miami-Dade Circuit Judge Stanford Blake set a hearing on the issue for Wednesday afternoon.