Federal agents returned to the City Hall offices of Ald. Ed Burke on Thursday, two weeks after they carried out unprecedented raids on the longtime alderman’s downtown and ward offices, sources said.

Federal investigators were looking for information they didn’t find during the first raid, sources said. The nature of the information sought was unknown.

On Nov. 29, federal investigators descended on Burke’s ward and City Hall offices and covered the windows with brown butcher paper. At City Hall, investigators spent at least five hours inside and left with boxes of records and computers.

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They also showed up at the home of political operative Peter Andrews Jr., the longtime head of Burke’s ward organization. They seized Burke’s cellphone.

Sources at the time told the Sun-Times that the initial raid was not triggered by Burke’s administration of the city’s $100 million workers compensation program, nor was it tied to Burke’s property tax appeals work for the Trump Tower.

However, what triggered the raids remains a mystery.

Burke could not be reached for comment Thursday night. Officials with the FBI could not be reached. A spokesman for the U.S. Attorney’s Office in Chicago would not comment.

After the initial raid, Burke denied wrongdoing.

“As you are aware, there have previously been several other investigations such as this. In every instance we cooperated fully. And in every instance nothing has been found,” Burke told reporters then.

“So once again we will be cooperating fully and I am completely confident that at the end of the day nothing will be found amiss in this instance either.”

The second raid was first reported by NBC5 political editor Carol Marin.

Over 50 years in politics, the 14th Ward alderman has faced — and survived — other investigations. Burke will celebrate his 75th birthday on Dec. 29.