Sheriff Louis Ackal trial

Iberia Parish Sheriff Louis Ackal smiles as he leaves the US District Court in Shreveport, La after he was found not guilty on all of the four counts he was being charged on.

A federal judge has ruled that an Iberia Parish Sheriff's Office deputy cannot withdraw his guilty plea in a sweeping investigation of civil rights abuses that also targeted Sheriff Louis Ackal.

Ackal, who laid blame on a group of rogue deputies, was acquitted at trial last year, but 10 of his men pleaded guilty in the case.

Bret Klein Broussard, who testified against Ackal, had sought to back out his February 2016 plea, arguing that the U.S. Justice Department official who signed off on the criminal charges against him didn't have the legal authority to do so.

U.S. District Judge Donald Walter, in an order filed Tuesday, shot down that argument, ruling that Broussard waived his right to challenge his conviction when he pleaded guilty.

Broussard's defense attorney, Brett Grayson, contended the plea was not valid because the assistant attorney general in charge of the Justice Department's Civil Rights Division at the time, Vanita Gupta, was never confirmed in the position by the U.S. Senate and therefore lacked the authority to sign off on the case.

Gupta served for several years in an "acting" capacity, staying in the position beyond the 210 days the defense attorney contends were allowed under a law known as the Federal Vacancies Reform Act.

Attorneys for a Chicago suburb seeking to dismiss a Justice Department fair housing lawsuit that was filed while Gupta led the Civil Rights Division, have recently raised a similar issue.

"I think that it's a pretty good argument," Grayson said.

Walter stated in his ruling that even had he found Broussard did not waive his right to challenge the guilty plea, the Federal Vacancies Reform Act would not apply in the case because, among other reasons, local U.S. Attorneys have independent power to enforce the law.

Grayson said his client has not decided whether to appeal Walter's denial.

Broussard was accused of not intervening while other deputies struck an inmate at the Iberia Parish jail with batons.

He and six other deputies who also pleaded guilty in the case are set to be sentenced on March 28.

An 11th deputy who did not plead guilty, Mark Frederick, is set for trial on the same day. 

Three of the deputies who have already pleaded guilty have been identified as possible witnesses in the case, and their sentencing hearings have been pushed back to April 21.

Frederick is accused of assaulting an inmate at the Iberia Parish jail in 2011.

He has also raised the Federal Vacancies Reform Act issue in a motion to dismiss the charges against him, but his case is being handled by Walter, who has already shot down Broussard's nearly identical argument.

Follow Richard Burgess on Twitter, @rbb100.​