A key figure in ousted Illinois Gov. Rod Blagojevich's federal corruption case died Saturday of an apparent "aspirin overdose," a law enforcement source told the Chicago Sun-Times.   

Christopher Kelly, 51, was Blagojevich's former chief fundraiser, and was described by the newspaper as "go-to" guy in the ex-governor's administration.  

His family found him early Saturday morning and was pronounced dead several hours later at Cook County's Stroger hospital, where he had arrived by ambulance, said spokesman Marcel Bright.  

An autopsy was to be performed.

On Tuesday, Kelly admitted he paid $450,000 in kickbacks to an unnamed consultant who allegedly inflated cost estimates for repairs to hangars operated by American Airlines and United Air Lines at O'Hare International Airport. He was sentenced to nearly 5 years in prison.

He admitted that bids on the projects were rigged to make certain that his BCI Commercial Roofing Inc. would land the contracts. In all, the contracts paid Kelly $8.5 million. His profit was $2.5 million, according to the plea agreement.

Kelly was expected to report to federal prision Sept. 18, according to MyFOXChicago. 

Days after his guilty plea, he said he was being pressured by the federal prosecutors to cooperate in their Blagojevich corruption investigation, the Sun-Times reported. 

Kelly was indicted on three separate federal cases, including the one that alleges Blagojevich sought to sell or trade President Obama's former seat in the U.S. Senate.

Kelly had pleaded not guilty in that case to charges that he plotted with Blagojevich even before his 2002 election to use the muscle of the governor's office as a moneymaking machine to squeeze payments out of those seeking state business.

Blagojevich was in New York when he learned of Kelly's death.

"I am deeply saddened to hear that Chris has died. My heart goes out to his wife Carmen, his three daughters Grace, Jacqueline and Claire and his entire family. They are in our prayers," Blagojevich said in a statement.

Click here to read more on this story from MyFOXChicago.com

Click here to read more on this story from the Chicago Sun-Times.

The Associated Press contributed to this report.