LAFAYETTE — An assistant district attorney and his secretary pleaded guilty Thursday in an ongoing federal probe of bribery in the local court system.

The pleas come after 15th Judicial District Attorney Mike Harson’s longtime secretary and office administrator, Barna D. Haynes, pleaded guilty to a count of conspiracy Monday in an investigation of bribes paid for favorable treatment, mainly in DWI cases.

On Thursday, Greg Williams, an assistant district attorney in Harson’s office, and Williams’ secretary, Denease Curry, both pleaded guilty in the investigation.

“There is no place for this kind of activity in the criminal justice system,” U.S. Attorney Stephanie Finley said in a written statement. “Both Williams and Curry were entrusted with the responsibility of ensuring that justice was served as it related to OWI cases. They grossly violated that trust.”

Finley has declined to comment on how many people might be targeted in the investigation.

Curry, Williams and Haynes have all agreed to cooperate with federal prosecutors as part of their plea deals.

Harson, who has not been implicated in the case, said both Williams and Curry resigned Wednesday afternoon. Haynes resigned in August.

“It’s disappointing, and I’m certainly sorry it happened,” Harson said Thursday. “Fortunately, as far as I know, that is the end of as far as my office is concerned.”

Williams, 44, pleaded guilty to one count of conspiracy.

He admitted to accepting at least one cash payment of $500 and a series of gifts that included an autographed New Orleans Saints hat, bicycles for himself and his family members, and clothing, according to court filings by prosecutors.

Curry, 46, pleaded guilty to one count of misprision of a felony for not reporting the bribery scheme when she had knowledge of it.

Curry also admitted in court filings to accepting about $1,600 for working with Haynes to coordinate the special state court plea agreements that were arranged in return for the bribes.

Haynes admitted accepting $55,000 in bribes — at $500 a case — but federal prosecutors contend the amount exceeded $70,000.

All of the money allegedly flowed from a person who has yet to be charged and who has been identified by prosecutors only as “co-conspirator No. 1.”

That person solicited “hundreds of thousands of dollars from individuals with criminal charges” on promises of getting defendants favorable treatment in the court system, according to court filings form prosecutors.

Prosecutors wrote that the bribery scheme lasted for about four years, from March 2008 until Feb. 27, the day FBI agents searched the District Attorney’s office.

Williams and Curry did not become involved until 2010, according to prosecutors.

Haynes, 58, admitted in court documents that, in return for the bribes, she routed criminal defendants into a special program in which their charges were quickly dismissed if they successfully completed certain probation requirements, such as drivers safety classes, substance abuse treatment and community service.

All of the deals arranged by Haynes were approved by the same state judge in special sessions handled by Williams, according to court filings from prosecutors.

Prosecutors did not identify the judge but stated in court filings that many of deals arranged by Haynes were formalized in that judge’s chambers rather than open court, where criminal cases are generally handled.

For DWI defendants, the quick resolution of the case through the special program could keep the charge off their insurance and, according to federal prosecutors, allow for the immediate reinstatement of driving privileges.

The special program itself was not illegal, only the bribery aspect, and Harson said other DWI defendants not connected to the federal case also participated.

The bribery scheme was carried out without Harson’s knowledge, in part because of a “lack of oversight and safeguards,” according to court filings by prosecutors outlining the allegations in the case.

Harson said Thursday that he feels there was little he could have done because he cannot personally supervise the roughly 100 staff members that work for him in the three parishes his office covers — Lafayette, Acadia and Vermilion.

“I have to delegate,” he said.

Haynes and Williams face up to five years in prison.

Curry faces up to three years.