CHICAGO (CBS) — The corruption trial of state Rep. Derrick Smith kicked off Thursday with opening statements and federal prosecutors saying they’ve got the goods on the Chicago Democrat.

CBS 2’s Derrick Blakley reports.

The case centers on Smith taking a cash bribe, a federal prosecutor said.

Smith, 50, is accused of taking $7,000 in exchange for writing a letter supporting a day care center’s application for a state grant.

“He wanted cash with no trace. He wanted no one to know about that bribe money,” Assistant U.S. Attorney Michael Donovan said.

Smith’s defense attorney, Victor Henderson, said the lawmaker wrote the letter thinking he was helping a constituent.

Henderson contends Smith was betrayed by an FBI informant who wore a wire. The informant was a down-and-out friend and ex-con named “Pete” who sold his allegiance for FBI cash, the attorney says.

“Each time Pete was coming to Derrick for money, he was also going to the FBI for money. When it was all said and done, the FBI paid Pete almost $25,000,” Henderson said.

Prosecutors argue Smith not only confessed but led agents to his home, where they recovered $2,500 of the FBI’s marked $100 bills.

Henderson said the lawmaker never considered pleading guilty in case.

Smith is now a lame-duck legislator. He lost his re-election bid in the March primary.

Prosecutors will begin playing secretly recorded tapes of Smith in court Friday. Federal Judge Sharon Johnson Coleman ruled against releasing them to the wider public.