A federal judge threw out the fraud conviction of Chicago's former streets and sanitation commissioner Tuesday and granted him a new trial on charges of illegally rewarding political campaign workers with city jobs.

Al Sanchez was convicted at the high profile trial based on testimony from a key witness whose arrest record and gang affiliations should have been disclosed beforehand to defense attorneys but were not, Judge Robert W. Gettleman said.

FBI agents based in Indiana also should have told prosecutors in Chicago that the witness, Brian Gabriel, was under investigation in a gang war between the Spanish Vice Lords and Latin Kings at the time of the trial, Gettleman said.

And the prosecutors could have learned of that investigation if they had performed a records search, Gettleman said in his 22-page opinion.

"Based on these findings, this court has lost confidence in the integrity of the verdict convicting these defendants," Gettleman said in his 22-page opinion.

Gettleman also ordered a new trial for a youthful former aide to Sanchez, Aaron Delvalle, who was convicted of one count of perjury at the March trial.

The trial attracted the spotlight because as streets and sanitation commissioner Sanchez headed a department that for decades was a major pool of patronage jobs for the once mighty Chicago Democratic Machine. That spotlight was intensified because in recent years the U.S. attorney's office has conducted a major investigation of hiring fraud at City Hall.

First Assistant U.S. Attorney Gary Shapiro said there would be no comment on Gettleman's decision.

"We are delighted," said Sanchez attorney Thomas M. Breen. "We should have been apprised of this witness's gang affiliations, we should have been apprised of his prior arrests, we should have been apprised that he was the target of a federal investigation at the time that he testified."

Witnesses testified that Sanchez took part in a scheme to reward members of the Hispanic Democratic Organization with city jobs. Hiring city employees based on their political background is illegal.

Besides his city post, Sanchez was a high-ranking official of HDO, a group that strongly supports Mayor Richard M. Daley.

Sanchez has denied that politics played a role in getting HDO members jobs.

Gabriel testified that he got a job as a streets and sanitation truck driver in 2000, two years after joining HDO as a "foot soldier." He said Delvalle was one of the HDO coordinators who gave him his marching orders.