Prosecutors have refused criminal charges against a private investigator hired by U.S. Sen. David Vitter who was caught spying last fall on Jefferson Parish Sheriff Newell Normand and several of his associates — a sensational arrest that caused a stir on the eve of Louisiana’s gubernatorial primary.

The investigator, Robert J. Frenzel, was booked in October on one count of criminal mischief, a misdemeanor, following a bizarre run-in at the Royal Blend coffeehouse on Metairie Road in which he surreptitiously recorded the sheriff’s regular coffee klatsch and, after a testy confrontation, fled from the business and ran through several private properties.

Vitter’s campaign acknowledged hiring Frenzel’s firm, J.W. Bearden & Associates, of Texas, to conduct opposition research, but it said the private eye had been sent to the coffeehouse to monitor John Cummings, a prominent lawyer and real estate investor who supported Gov. John Bel Edwards in last year’s lively campaign. Cummings also was present at the coffee confab.

The Jefferson Parish District Attorney’s Office refused the case against Frenzel “on grounds of insufficient evidence,” said Paul Purpura, a spokesman for District Attorney Paul Connick.

The decision had been expected among local law enforcement officials, even though Normand said publicly last fall that he was considering booking Frenzel on an additional count of violating the state’s wiretapping law.

The sheriff also said at the time that he had discussed the coffeehouse recording with the FBI. He said he turned over a number of investigative materials to the bureau, which did not immediately respond to a request for comment Monday.

“Mr. Frenzel is pleased to put this matter behind him,” said David Courcelle, Frenzel’s defense attorney. Frenzel remains employed as a private investigator with the same firm, Courcelle said.

Connick’s office offered no further comment Monday on its reasons for refusing the charges.

Normand, in a phone interview Monday, said he was not surprised by Connick’s decision. He said there was “no doubt” Frenzel had committed trespassing as he fled but added, “I don’t know that there was anybody aggrieved.”

“It doesn’t rock my world in the least bit,” the sheriff said of Connick’s action. “We don’t need to be wasting the time of the criminal justice system on this.”

“I’m not looking to hurt this young man,” Normand added. “He was hired to do a job and was working for somebody else. We were trying to get to the bottom of what was going on, and he was refusing to talk and that’s why we arrested him.”

Normand, a longtime Vitter foe who backed Edwards, used the arrest to slam the senator in the weeks before the November runoff, holding a 50-minute news conference in which he showed reporters two small devices Frenzel had used to record him and the others at the cafe.

Normand also told reporters that video seized from Frenzel showed operatives from the Vitter campaign asking a woman to discredit claims a prostitute made about the senator.

The coffeeshop incident, which became known as “Spygate,” happened Oct. 23, just one day before voters cast their ballots in the primary, in which Vitter finished a distant second behind Edwards. Fallout from the episode dogged Vitter during the monthlong runoff campaign.

At the news conference Normand held at the time, the sheriff said he first noticed Frenzel was recording him in the cafe when he leaned in to say something to Cummings, who has trouble hearing.

“It was at this time the sheriff noticed that (Frenzel) became nervous and began to fumble with his phone, which allowed the sheriff to physically observe the display of the phone with a recording application activated,” a Jefferson Parish Sheriff’s Office report says. “The sheriff challenged the subject as to why he was filming him.”

Several deputies were called to the area and ultimately found Frenzel hiding behind an air-conditioning unit in the 100 block of Stella Street. The private investigator eventually “confirmed that he was on an assignment to conduct surveillance on a subject with a white beard,” the report says, an apparent reference to Cummings.

“We didn’t know what he was doing,” Normand said. “We wanted to figure out why he was running from us. It was just unusual behavior.”

At the time, the Vitter campaign accused Cummings of paying for “false testimony” against the senator. Campaign officials announced that they, too, had turned over various materials to the FBI.

Follow Jim Mustian on Twitter, @JimMustian.