One of 10 deputies who admitted wrongdoing in a broad federal probe of civil rights abuses at the Iberia Parish Sheriff's Office has asked a judge to void the guilty plea he entered in the case last year.

Bret Klein Broussard, a former narcotics officer who as part of his plea deal testified against Sheriff Louis Ackal, argues in court filings 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.

Ackal was acquitted at his trial last year, but ten of his deputies pleaded guilty and charges are pending against an 11th.

Broussard was accused of standing by and doing nothing while other deputies struck an inmate at the Iberia Parish jail with batons, among a long list of abuses alleged in the federal investigation.

The former deputy pleaded guilty in February 2016 to a federal charge of deprivation of rights.

But his defense attorney argues in court filings that the plea is not valid because the assistant attorney general in charge of the Justice Department's Civil Rights Division at the time, Vanita Gupta, did not have the authority to sign off on the case because she was never confirmed in the position by the U.S. Senate.

Justice Department attorneys labeled Broussard's legal argument as "novel and far-fetched."

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

The legality of her tenure has been called into question by conservative news outlets, including The National Review, and the issue has arisen in at least one other recent case: a Chicago suburb seeking to dismiss a Justice Department fair housing lawsuit that was filed while Gupta led the Civil Rights Division.

Justice Department attorneys contend in court filings that Broussard's legal argument to void his guilty plea amounts to a misinterpretation of the Federal Vacancies Reform Act.

Regardless, they argue, the local U.S. Attorney's Office has authority to pursue civil rights cases on its own without the authorization of higher-ups in Washington, D.C., and Broussard gave up most of his rights to challenge his conviction when he pleaded guilty.

"The defendant may regret his knowing and voluntary decision to enter into a plea and confess to years of brutality and misconduct. However, there is no fact and no legal theory, real or contrived, that permits him to escape the consequences of his decision," Justice Department attorneys wrote in court filings.

The judge has set no timeline for a decision on the issue, but Broussard is set to be sentenced March 28.

He faces up to 10 years in prison, but he would likely receive much less under the guidelines that govern federal sentencing.

The federal investigation against Ackal stretched back to his first months in office in 2008 and included allegations that he turned a blind eye and sometimes encouraged the abuse of inmates and the rough treatment of suspects in street-level narcotics enforcement.

Ackal, who remains sheriff, argued that any abuses were carried out by rogue deputies who worked to conceal their actions.

Follow Richard Burgess on Twitter, @rbb100.​