A federal judge in New Orleans has dismissed a whistleblower lawsuit filed last year against St. John the Baptist Parish Sheriff Mike Tregre by his former chief deputy, who alleged he was terminated after raising questions about a network of hidden cameras in the sheriff’s interrogation rooms.

U.S. District Judge Carl J. Barbier’s ruling, issued Thursday, came a year after a State Police investigation concluded that the cameras did not necessarily violate state law, although it said the equipment could have been used improperly.

In his 21-page ruling outlining his reasons for dismissing the lawsuit, Barbier said neither side disputed that the Sheriff’s Office’s three interrogation rooms were equipped to record audio and video. But Barbier said Tregg Wilson’s lawsuit did not meet the needed benchmarks for securing a First Amendment defense for speaking out about his concerns because he was doing so as a high-ranking Sheriff’s Office official, not a private citizen.

“If the court finds that the employee did not speak as a citizen on a matter of public concern, there is no First Amendment protection,” Barbier wrote.

By virtue of his position, Wilson was required to report the cameras if he believed they were being used for potentially illegal recordings, and his actions were part of his job responsibilities, the judge said.

Tregre declared victory Monday. “The investigation and the judge’s ruling both confirmed that we were conducting business properly, as it is supposed to be done,” he said.

As part of his probe, the State Police investigator who filed the report, Trooper Oliver Jackson, contacted officials in three district attorneys’ offices, who said they thought the hidden cameras — which have since been removed — did not violate the law because there is “no expectation of privacy within an interview room of a police or sheriff’s department.”

But the cameras “could very well violate the law if used in an unlawful manner,” the report added.

“I was informed that an example of misuse would be for law enforcement to intentionally place an attorney and his client in an interview room, and secretly record the conversation of privileged information divulged by the suspect to his attorney for the purpose of furthering their investigation,” Jackson wrote.

The report said no evidence surfaced that detectives resorted to such trickery, or even thought about it.

Tregre, who took office in July 2012, said the equipment was installed by his predecessor and he was unaware of it until months before the lawsuit was filed by Wilson, a lawyer and formerly Tregre’s chief deputy.

Wilson told Jackson he had learned that the department’s interrogation rooms were rigged with hidden cameras that ran on a continuous feed. Though the cameras were designed to capture interviews of criminal suspects, Wilson noted that they might also record conversations between suspects and their attorneys — which would be illegal and could jeopardize criminal prosecutions.

The backup cameras were motion-activated, court filings show.

The audio and video were captured on a server and retained for 30 days.

Tregre filed for summary judgment dismissing the suit on Aug. 12, and Barbier granted it last week. Wilson said Monday that he expected to appeal the judge’s ruling.

Follow Richard Thompson on Twitter, @rthompsonMSY.