The FBI had wanted to hold off on arresting the Cannibal Cop until there was more clear-cut evidence that he was not just engaging in fantasy when he schemed online with other sickos to kidnap, rape, torture, murder, cook and eat numerous women.

The next step for the FBI might well have been to introduce an undercover, as is often done in pedophile cases that originate on the Internet.

But Gilberto Valle was a real-life New York City police officer, and the NYPD did not want a guy walking around with a gun and shield who spent his off-duty hours discussing even imaginary plans to commit the unimaginable against women who had real names and faces.

The NYPD really had no choice to but insist that the FBI make the collar. And, just a month after the investigation began, the FBI did exactly that.

“The PD shut it down,” a federal law enforcement official said afterward.

The arrest created a sensation. Fellow cops at the 26th Precinct in upper Manhattan wondered if they really had been working with a cannibal. Many of us did not even know the cyber realm harbored such depravities. Some felt that Valle was being prosecuted not for what he did but for what he said online. It all seemed a true tale of our times.

“The highly unusual facts of this case reflect the Internet age in which we live,” Manhattan Federal Judge Paul Gardephe later noted.

The immediate legal result was a conviction in Manhattan federal court for conspiracy to commit kidnapping, an outcome that surprised even some federal law enforcement officials.

“It’s a tough case,” one had said as he listened to the final summations.

That was last year. The defense pledged to appeal, and this week a federal judge threw out the conviction due to a lack of persuasive proof that Valle had engaged in anything more than online fantasy. That is not in itself a crime, no matter how repulsive.

“The evidentiary record is such that it is more likely than not the case that all of Valle’s Internet communications about kidnapping are fantasy role-play,” Judge Gardephe said in his 118-page ruling.

The judge noted that in his online profile, Valle stated, “I like to press the envelope but no matter what I say, it is all fantasy.”

During his 18 months of what could have been a life sentence behind bars, Valle had found what are likely the only circumstances on earth where anybody would put him to work as a cook. He was competent enough to have continued in that capacity, though all but the most depraved inmates likely found it necessary to block from their minds his oft-repeated desires to slowly roast a woman alive.

When he was formally freed on Tuesday, Valle emerged into the sunshine from the courthouse in downtown Manhattan with a prison pallor and a smile. He had traded his convict uniform for civilian attire, though he still had on prison-issue footwear. One of his relatives joked that at least he had gotten a new pair of shoes out of the deal.

At one point, Valle offered an apology to anybody who had been “hurt, shocked or offended by my infantile actions.” He seemed back to being the polite and considerate man his now-former wife had dated after meeting him via an online matchmaking service.

“It was nice, he opened doors, he pulled out chairs,” Kathleen Mangan had testified during the trial.

Mangan recalled that Valle had begun to change after she became pregnant in the fall of 2011. He would return from working a 3 p.m.-to-midnight shift and retreat into TV, video games, and, increasingly, the Internet.

“He started staying up really late, or not coming to bed at all,” she testified.

Things got only worse after they were married the following June.

“The wedding was nice,” she recalled on the stand. “The marriage was not.”

That August, Mangan went on the MacBook laptop they shared and discovered that he had forgotten to log out. She saw he had been on a website called “Fetish Net.”

“The girl on the front page was dead,” Mangan told the court.

Mangan confronted her husband, but he continued to stay online through the night while she and their infant were in bed. The marriage was even more not nice.

In September, Mangan installed spyware on the computer that recorded all her husband’s online activities. She became so alarmed by the result that she fled the couple’s apartment in Queens with their baby daughter.

From her parents’ home in Nevada, Mangan continued to monitor his online life and came across an exchange in which Valle spoke of butchering her. She testified, “I was going to be tied up by my feet and my throat slit, and they would have fun watching the blood gush out of me because I was young.”

One of Valle’s online pals had said, “If she cries, don’t listen to her, don’t show her mercy.”

Valle had replied, “It’s okay, we will just gag her.”

She also had come across photos of real women her husband knew, along with talk of torturing and raping them. She saw that Valle posted at one point “it’s fantasy,” but she remained frightened enough to take what she had to the FBI.

The judge recounted all of this in Monday’s decision, along with his memories of when the wife took the stand.

“During her testimony against her husband, a courtroom filled with hundreds of spectators sat rapt with attention,” the judge wrote. “Both Mangan and Valle cried, requiring the Court to recess. Valle’s wracking sobs echoed throughout the courtroom.”

The judge went on, “In this Court’s 30-year experience in courtrooms as a lawyer and as a judge, Mangan’s testimony ranks as some of the most dramatic. Undoubtedly, it made a powerful impression on the jury.”

The jury also no doubt took note of a moment during defense attorney Julia Gatto’s otherwise masterful summation when she sought to explain why Valle had used a law enforcement database to obtain the personal information of a woman who was a subject of the sicko cyber talk. Gatto lamely maintained that Valle had just been checking the system.

“To make sure it’s working,” she said.

The judge let stand the conviction on the much lesser charge of unauthorized use of the database, which the FBI might have been able to establish as a step toward making fantasy real had it been able to hold off on an arrest and introduce an undercover.

But the NYPD had been obliged to shut it down. And all the shock and sobs and drama of the trial did not change the judge’s view that the evidence was insufficient.

Outside court on Tuesday afternoon, Valle looked and sounded like the young man his wife thought she knew before she really came to know him.

After quietly offering his apologies, Valle headed off to eat the pastellas his mother made at Christmas and has been keeping in the freezer with the hope he would be freed.

His mother was beaming and seemed to take the acquittal as a vindication.

But what mother could accept that her son had often said the food he really wanted to eat was not one of those lovingly mom-made Spanish meat pies but women he cooked after raping them and subjecting them to unspeakable tortures?

At least the judge ordered him to stay away from computers.