A source familiar with the investigation said the FBI began investigating Solis in 2014 and 2015 for allegations he was misusing campaign funds for personal use.
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The source told ABC7 that a search warrant was served on Solis' home and another location where the campaign money was spent. The feds then leveraged Solis and convinced him to wear a wire when speaking with Burke.
"Generally when you see somebody wearing a wire against somebody else in a criminal investigation, it's because they felt that they had to," said ABC7 Legal Analyst Gil Soffer. "It's because the government has some leverage over them. Maybe even the government threatening prosecution or promising some leniency in exchange for cooperation."
Solis announced he was not running for reelection less than a week before federal investigators raided Burke's office. He did not return multiple calls and texts seeking comment.
ABC7 has also learned that Solis' 25th Ward organization donated $55,000 to the campaign of Illinois Comptroller Susana Mendoza, who is now running for mayor. Mendoza's campaign said she will be donating the money to charity.
"I will be, now that the developments have been brought to my attention about potential wrongdoing on Alderman Solis' part, immediately contributing the donations that he's contributed to me over many years of public service to a very worthy cause," Mendoza said.
The Chicago Sun-Times initially reported the secret recordings.
The Sun-Times report said Solis has been working with law enforcement officials to secretly recording conversations with Burke over the last two years. That apparently helped authorities build their corruption case against him.
City Council reacts to news Ald. Solis secretly recorded Ald. Burke
Aldermen reacted to the news ahead of Wednesday's City Council meeting, and while Solis was a no-show, Burke was there. For the first time in decades, Burke was not front-and-center as chairman of the finance committee.
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The typically long-winded alderman didn't say a peep when he was met by a group of reporters asking him about the reports of Solis wearing a wire.
"I've done nothing wrong and anything Alderman Solis recorded, if he did, isn't going to make a difference," Burke said.
The news of Solis, who is chairman of the zoning committee, recording Burke was seen as an act of betrayal by some, but not all.
"I'm disappointed that he let down his community, the simple fact that something occurred in order to put him in that position," said Alderman Gilbert Villegas, Latino Caucus Chairman. He said Solis should resign immediately.
Some assume Burke may not be the only one caught on tape doing something wrong.
"If you're one of those alderman that is working for a rigged system that's been selling your clout for campaign contributions, that's been selling your clout in order to get richer, you should be worried," said Alderman Carlos Ramierz-Rosa, 35th Ward.
"I look at it as the tip of the iceberg that's going to prove what we have been doing and what we've been saying for many years is the right thing," said Alderman Scott Waguespack, 32nd Ward.
"Our concern is how much has been going on for the last two years?" said 45th Ward Alderman John Arena. 'We have massive TIFs being discussed with finance, with zoning, we need to put a brake on a whole lot of things and take a really close look at that has been going on in this building and it's troubling."
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RELATED: Ed Burke, longtime Chicago alderman, charged with attempted extortion
Waguspack said this is an opportunity to push ethics reforms that have been rejected by Burke and the mayor in the past. Mayor Rahm Emanuel said reforms will be his focus as well.
"The question is given what we do know if this is confirmed, what are we going to do that is what I'm going to spend my energy and time making changes," said Emanuel.
Emanuel also said he doesn't think Solis should resign, despite calls for him to do so. He said the fact that Solis made the decision not to run for reelection speaks for itself.
Burke, 75, is charged in a federal criminal complaint with attempted extortion, for alleging shaking down a Burger King Franchise owner looking to renovate their Southwest Side restaurant. Wednesday's City Council meeting is its first full meeting since Burke was charged.
RELATED: Feds request more time to indict legendary Chicago Alderman Ed Burke
The feds have asked for a 90-day extension to put the investigation in order for a grand jury to indict Alderman Burke.
Alderman Burke stepped down as City Council Finance Committee chairman shortly after the complaint against him was filed. He has denied any wrongdoing and is seeking re-election.