ST. LOUIS — Missouri state Rep. Talibdin "T.D." El-Amin was so afraid that listening devices had been planted in his district office that he refused to talk about accepting a bribe.

Trading notes about it, however, was a different matter.

"How much can you come up with today," he wrote during a meeting with a gas station owner who was having trouble with his local alderman.

"$500 OK?" the gas station owner replied before slipping El-Amin the amount in cash.

What El-Amin didn't realize: Not only were federal agents listening to his conversation, they also were watching via a hidden camera, capturing his note exchange with the gas station owner, who was cooperating with the government.

On Thursday, the St. Louis Democrat pleaded guilty on one count of soliciting and accepting a bribe, a felony that calls for a prison sentence of 18-24 months.

El-Amin, whose district covers northwest St. Louis, becomes the latest public official ensnared in a crackdown by the FBI's local anti-corruption squad.

A month ago, former state Sen. Jeff Smith, of St. Louis, and former state Rep. Steve Brown, who represented Clayton, resigned after admitting their role in a political cover-up aimed at an election opponent.

El-Amin's case does not appear to be directly related to Smith and Brown, but it may have tentacles that reach further into city politics. Court documents quote El-Amin as saying he was also soliciting a bribe on behalf of a City Hall department head. The plea agreement also suggests the alderman who originally targeted the business owner was doing so, in part, because the individual did not contribute to the alderman's fundraisers.

Federal officials declined to name the alderman, the city official or the gas station owner, who was identified in court documents as "John Doe." Officials also would not say whether the investigation concluded with El-Amin's plea.

Local FBI chief John Gillies did say other corruption investigations are ongoing and that elected officials should heed a lesson from El-Amin's downfall.

"Politicians: Take the 'For Sale' sign down," Gillies said.

El-Amin said after his court appearance that he had turned in his resignation. A spokesman for the governor's office said it was not yet in hand Thursday evening.

El-Amin, 38, was first elected in 2006 and won a second term last year. He appeared upbeat in court Thursday. Asked by the judge how he was doing, El-Amin responded, "Feel great."

El-Amin was joined in the courthouse by his wife, Yaphett, who previously held the same state House seat. Her father, a minority contracting consultant, is already in federal prison on tax evasion charges.

Later, on the courthouse steps, T.D. El-Amin offered remorse.

"I apologize to my family, to my friends and those who have supported me," El-Amin said. "Although I may not walk the halls of Jefferson City, I do still plan on walking the streets of St. Louis and serving the people."

El-Amin is accused of accepting $2,100 in cash bribes. He asked for an additional $1,500 — $500 for himself, $1,000 for the unidentified city official — but never collected, according to the plea agreement.

The owner of the gas station and convenience store first approached El-Amin in March, after he began feeling the brunt of increased city inspections.

The gas station owner, according to the plea agreement, believed he was receiving city court summons and nuisance violations "at the behest of his alderman as the direct result of his failure to contribute to the alderman's fundraisers and another incident."

On April 24, the gas station owner told El-Amin over the phone that the alderman "is just trying to destroy me. I need your help," according to the court document.

On May 1, El-Amin and the gas station owner met in El-Amin's district office on Union Boulevard, where the gas station owner offered to give El-Amin $500. El-Amin, in turn, slipped him a note.

"I absolutely don't talk $ in this office," it said, according to the plea agreement.

After accepting the first $500 in cash, El-Amin then slipped the owner another note, indicating he wanted three more payments through July 15.

In the same conversation, El-Amin explained why he preferred written communication.

"Not something I'm very comfortable talking about, money," El-Amin said, according to a transcript in the court documents. "For me to say that I'll do this for that would be a violation, so I don't ever want to talk about helping and attaching that to money."

The court documents say El-Amin kept all of his handwritten notes after the meeting.

At subsequent meetings, according to court documents, El-Amin told the gas station owner that he had spoken to city officials on his behalf — including the unidentified department head — and expressed his desire to be able to give the department head $1,000 of the bribe money.

"Now, what I'd like to do is be able to say, 'For Father's Day, here's a grand,'" El-Amin said.

The court documents contain no proof that El-Amin ever had any actual contact with the City Hall official, other than El-Amin saying the department head "called me back" and "that he's taking this seriously."

Mayor Francis Slay's office promised a thorough review to determine whether any city officials were involved in El-Amin's bribery scheme.

"The city counselor and I are reviewing every document and interviewing every city employee who had anything to do with enforcing nuisance property ordinances," Slay's chief of staff, Jeff Rainford, said in a statement. "There is no indication that any city employee tried to intervene inappropriately to either help or hurt the gas station owner; or that this is anything other than Mr. El-Amin's story to his target."

Rainford promised to act "decisively, forcefully and publicly" if any wrongdoing is uncovered, "even if it is not a crime."

While court documents do not identify the alderman, 27th Ward Alderman Gregory Carter said Thursday that it could be him.

"It's a possibility," Carter said.

Some of Carter's ward is in El-Amin's state House district. Carter also has had a long-running feud with a gas station owner near the intersection of Goodfellow Boulevard and Interstate 70.

In 2007, Carter was assaulted at the station after an altercation with a man aggressively peddling CDs and DVDs inside the convenience store. Carter has criticized the business but said he was motivated by safety, not a lack of political contributions.

"This guy, he is definitely going through our nuisance program," Carter said.

A man who identified himself as the owner of the gas station declined to comment on Thursday. "I don't want to give anything," the man said.

Once El-Amin's resignation is official, Gov. Jay Nixon is expected to call a special election to replace him. It will be the second such local contest Nixon has called in recent weeks — a special election is set for Nov. 3 to replace Smith and Brown. But it's too late for that election to include El-Amin's seat, according to state election guidelines.

Ironically, El-Amin had been lobbying for the nomination to replace Smith in the Senate but dropped out as questions over potential legal troubles grew.

His conviction comes amid mounting speculation about other public officials who may be the subject of law enforcement inquiries. St. Louis License Collector Michael McMillan has acknowledged that the U.S. Treasury Department asked him for personal financial documents. In Clayton, St. Louis County Executive Charlie A. Dooley angrily denied his office was the subject of an investigation after a top aide, Darin Cline, abruptly resigned this week.

State Rep. Joe Smith, R-St. Charles, said Thursday he has worked alongside El-Amin and that he has viewed him as "a good guy."

"This is a bad situation," Smith said. "It's a black eye for members of the General Assembly. ... People ask, 'What are they doing in Jefferson City?'"

Elizabethe Holland and Robert Patrick of the Post-Dispatch contributed to this report.