The portrayals of former New Orleans police Officer Donald Nides offered in federal court Monday could not have been more different.

To hear prosecutors tell it, Nides was a greedy cop who leveraged bribes of cash and oral sex from the operator of a shady pain clinic in Metairie even as his colleagues on a U.S. Drug Enforcement Administration task force entrusted him to root out prescription pill abuse in the area. Assistant U.S. Attorney Harry McSherry, pointing a finger at Nides on the first day of his trial in U.S. District Court, derided the 34-year NOPD veteran as “a double agent.”

“It’s about the cash, the greed,” McSherry told jurors in his opening statement. “It’s about the lust, the oral sex that he got as a result of providing the protection.”

Defense attorney Arthur “Buddy” Lemann, in equally impassioned opening remarks, dismissed the government’s case as overzealous and bereft of evidence, a “complicated, convoluted” prosecution that he said “really makes little sense.” He described his 64-year-old client as a committed husband who became known as “Detail Don” within the New Orleans Police Department because of his willingness to work extra-duty details.

“They do have it out for this man. There’s no doubt about it,” Lemann said, referring to the authorities. “They have to prove beyond a reasonable doubt that he intentionally corrupted a badge that he’s worn proudly for 40 years.”

The case may hinge upon the believability of Tiffany Miller Gambino, a 43-year-old co-defendant in the sprawling drug conspiracy who admitted last week to running a “pill mill” operation out of a sham pain clinic and who has agreed to testify against Nides.

Gambino, who claims she performed oral sex on Nides in exchange for law enforcement protection and frequent pointers on avoiding detection of her operation, has admitted paying Nides regular installments of cash between mid-2004 and May 2008, at times delivering it to him while he worked private details .

She’s also expected to offer the most salacious testimony of the trial. McSherry promised jurors a full accounting of the sexual activity, which he said occurred in various locations. “The oral sex was not just in the kitchen,” McSherry said. “The oral sex also happened in his car.”

Employees at the Omni Pain Management clinic took notice of the trysts, McSherry said. Before one illicit encounter, Gambino, applying makeup, asked a staffer to stay after hours and “guard the door” because she was expecting “Mr. Don” to be at the clinic late. “I don’t know a lot about makeup,” McSherry said, “but I’m told when you’re putting some makeup on, you’re expecting something.”

Prosecutors intend to present phone records that show 150 hours of calls between Nides and Gambino over a span of several years, including several calls that, due to their timing, suggest Nides had leaked information to Gambino in February 2008 about the DEA’s plans to conduct a raid the next day at another pain clinic managed by Gambino’s sister.

Nides is charged with conspiring to dispense prescription pills, obstruction of justice and lying to federal agents. McSherry said he gave deceitful answers in three interviews with law enforcement, insisting he’d never received oral sex.

According to McSherry, Nides admitted to federal authorities that he knew Omni had been a pill mill but that he didn’t feel it was his job to report the activity because his focus on the DEA task force had been detecting patterns of “doctor shopping,” a practice in which narcotics abusers go from doctor to doctor seeking the same prescriptions.

“All these times, he was there watching the addicted, the afflicted, the impaired,” McSherry said, accusing Nides of never alerting his colleagues at DEA.

Lemann, the defense attorney, urged jurors to be skeptical of Gambino, who faces up to 40 years in prison after admitting to the drug conspiracy and money laundering but who could receive a more lenient sentence in exchange for her testimony. “That’s called purchased testimony,” Lemann said, adding that she has changed her testimony from her initial statements. “Not only is she testifying with the hope of saving her own skin,” he said, “she’s also an admitted addict.”

Jurors also will likely hear from Dr. Joseph Mogan, who pleaded guilty alongside Gambino last week and is also facing a sentence of up to 40 years behind bars. Both the prosecution and defense spoke disparagingly of Mogan, with Lemann calling him “really pathetic” for flouting the Hippocratic Oath and McSherry lamenting that the University of Texas medical graduate “could have done good if he wanted to, but it was about greed.”

“It was about cash,” the prosecutor added. “It was the same thing that what got Donald Nides.”

The proceedings promise to open a window into the seedy world of pill mills, which prosecutors say became a grim reality for years at Omni Pain Management in Metairie and Omni Pain Management Plus in Slidell, both of which shut down last year after the authorities searched their premises. The clinics, which accepted only cash, drew patients from out of state who would wait long hours to be seen.

According to prosecutors, the clinics frequently issued prescriptions for “the holy trinity,” a cocktail of painkillers that combines hydrocodone, a sedative and a muscle relaxant.

Nides, visiting one of the clinics repeatedly under the guise of collecting “doctor shopping” information, would allegedly warn the clinics at times to cut back on certain prescriptions he knew would raise suspicion among his colleagues on the DEA task force.

Nides, after he was confronted by authorities, admitted he would not be surprised to learn there hadn’t been any prosecutions based upon the information he collected from the clinics, McSherry said. “Why were you continuing to go back there if there were no doctor shopping prosecutions?” he added in his opening statement.

Lemann said jurors would come to know Nides as “almost a miser” and “extremely hard-working,” noting Nides had once been hired to work as a security officer in the very courthouse where he’s being tried.

“Suspicion is one thing,” Lemann said. “Guilt beyond a reasonable doubt is something else, something much different.”

U.S. District Judge Susie Morgan said the trial is expected to last all week.

Follow Jim Mustian on Twitter, @JimMustian.