A Lafayette private investigator who charged clients as much as $5,000 per case to grease the wheels of justice with bribes and gifts for District Attorney employees was sentenced Friday to more than six years in prison.

Robert Williamson, 67, was snared in a federal investigation that also netted three employees of the DA’s office and is blamed with longtime District Attorney Mike Harson’s failed bid for re-election last year.

Williamson pleaded guilty in June to charges of conspiracy, bribery and Social Security fraud as a jury was being selected for his trial, admitting he received at least $443,000 from 2008 to 2012 to secure special plea deals for his clients by paying off employees at the DA’s office.

“He destroyed our faith, Acadiana’s faith, in our system of law,” said federal prosecutor Luke Walker in asking U.S. District Judge Elizabeth Foote to hand down the maximum sentence under federal guidelines — 78 months.

The judge complied.

Williamson, who has suffered a string of health setbacks in recent years, stood before the judge with the help of a walker as Foote outlined the details of the allegations and spoke of how he undermined faith in the legal system.

“The public must believe that the process of law and the rule of law are applied equally to all,” she said.

Williamson made only brief comments, telling Foote he was “greatly sorry for what I caused.”

Most of the bribes Williamson doled out were to secure special DWI pleas that allowed for charges to be quickly disposed of and expunged from the public court record.

“People who should have been dissuaded from drunk driving by receiving jail time and other penalties were instead given a pass to endanger lives again and again,” U.S. Attorney Stephanie Finley said in a written statement.

Williamson’s sentence was the stiffest of the six people charged in the case.

Barna D. Haynes, 61, Harson’s longtime secretary and the wife of Lafayette City Prosecutor Gary Haynes, was sentenced in July to 18 months in prison.

Williamson paid her at least $55,000 over four years — at $500 a case — for the inside touch needed to secure special treatment from the DA’s office for his clients.

Critical evidence in the case was drawn from wiretap recordings federal investigators made from late 2011 through early 2012 of exchanges between Williamson and Haynes.

In one, Haynes threatened one victim of an attack with criminal charges herself if she did not drop a complaint against one of Williamson’s clients, according to testimony earlier this year from FBI agent Doug Herman.

In another, Haynes is heard telling Williamson to start sending more cases her way because “we need some Christmas money,” Herman said.

Two other former District Attorney’s Office employees were tagged in the federal investigation for lesser roles.

Former Assistant District Attorney Greg Williams, 47, and his former secretary, Denease Curry, 49, both received two years’ probation.

Williams accepted $500 and a series of gifts — an autographed New Orleans Saints hat, bicycles and clothing — for overseeing plea deals for Williamson. Curry made about $1,600 for helping coordinate the special pleas.

Walker, the federal prosecutor, said all three DA employees had spotless records before Williamson “enticed” them with cash and gifts.

“He destroyed all their lives. These were people with long careers in public service,” Walker said.

Two former employees of the Acadiana Outreach Center, 64-year-old Sandra Degeyter and 62-year-old Elaine Crump, also were swept up in the scheme.

Degeyter, who received two years’ probation, admitted falsifying certifications showing criminal defendants had completed court-mandated community service at the nonprofit agency, which at the time provided assistance for the homeless and recovering addicts.

Prosecutors said Williamson paid her to provide false community service certificates, which were placed in court files to make it appear defendants had met the requirements for the special plea deals.

Prosecutors said Crump took over Degeyter’s job at the agency at some point, and Degeyter paid Crump to be allowed to forge Crump’s signature to continue producing the false community service certificates for Williamson on Acadiana Outreach letterhead, according to the court filings.

Crump, who pleaded guilty to misprision of a felony for not reporting the falsification of documents, also was sentenced to two years’ probation.

Harson was not identified as a target of the investigation, but federal prosecutors said a “lack of oversight and safeguards” at the DA’s office allowed the scheme to go unnoticed.

The scandal was a central issue in an election campaign that ended last year with retired prosecutor Keith Stutes defeating Harson, who had held the seat for two decades.

In addition to the prison term, Foote ordered Williamson to pay $77,677 in restitution to the U.S. Social Security Administration in connection with the Social Security fraud charge he faced for not reporting fees he received for arranging the special plea deals, income he was required to disclose to the government because he was receiving disability benefits.