On Nov. 20, the day after Rolling Stone published an account filled with allegations so lurid they ignited a national controversy, a college woman’s phone rang. It was the Charlottesville police calling. They wanted to talk to an allegedly traumatized woman named “Jackie.” The University of Virginia student agreed to discuss her story that multiple Phi Kappa Psi frat brothers raped her. But two weeks later, she clammed up, declining through a lawyer to answer any questions.

That was the last time the cops had any real contact with Jackie. So for the next five months, they did their investigation the hard way, checking bank accounts, phone records and photographs. It ultimately produced a report that methodically challenged every one of Jackie’s allegations, providing the first official undermining of the contested article.

It would probably play a significant role in any potential litigation brought by Phi Kappa Psi against Rolling Stone or the article’s author, Sabrina Rubin Erdely. A lawsuit appears to be under consideration. “Phi Kappa Psi is now exploring its legal options to address the extensive damage caused by Rolling Stone — damage both to the chapter and its members and to the very cause upon which the magazine was focused,” the chapter said in a statement, calling the article “defamatory.”

Indeed, the chapter, if not the wider campus, was wrongly made the focus of a heated national debate on the issue of campus rape and whether schools are doing enough to combat it. Some on the University of Virginia faculty are already calling for a lawsuit.

“I have expressed the view that the fraternity ought to sue Rolling Stone (and its writer individually),” Bob Turner, a professor of national security law and the author of an opinion piece calling for litigation, wrote The Washington Post in an e-mail. “As I recall from law school decades ago … falsely accusing someone of committing a heinous criminal act is defamation per se, and specific harm doesn’t need to be proven. … My guess is Rolling Stone is not going to want to see a drawn-out lawsuit covered by other media that they will certainly eventually lose.”

This seems a reasonable conclusion. But according to other legal experts, successfully litigating a libel case against Rolling Stone would be substantially more complicated than that and could expose the fraternity to further unwanted publicity.

Any libel lawsuit that doesn’t get thrown out right away on technical grounds would be accompanied by a lengthy, granular discovery and deposition process. That process would likely expose any fraternity’s “skeletons in the closet,” Rodney Smolla, a University of Georgia law professor who has worked libel cases, told the National Law Journal. “This could backfire on you,” he said. “If you’ve got things you’re not proud of that are there, then do not bring the case because all of that will come out and it will cause you more damage than good.”

Charles Tobin, a Washington attorney who specializes in libel law and writes frequently on the subject, told The Post that if the fraternity sues Rolling Stone, it would be a “colossal mistake.” He said there were several reasons for that prognosis. For one, he said, it has already gotten the public exoneration it was seeking. Plus, he too would be worried about “skeletons in the closet.”

“If they bring a lawsuit, they are opening up every young man in that fraternity to scrutiny — their drinking habits, and I’m sure some of them are underage, their sexual habits, and their overall conduct,” he told The Post. “It just seems like there’s a whole host of issues that could be there, and it would be unfair and unwise to subject these young men to that.”

Then there’s another problem that could prevent such a suit from going forward at all: Large groups generally cannot sue for defamation. The Rolling Stone article doesn’t specifically name any student beyond pseudonyms and descriptions that aren’t matched by any member of the frat house. Rather, the article slams an entire fraternity, sinking any potential lawsuit into some legally murky waters.

“A large group of undifferentiated people do not have a valid claim,” Tobin said. “And from my recollection of the article, it would be difficult for any one person to claim that they were defamed.”

For any group to have a justifiable claim, wrote Ellyn Tracy Marcus in the California Law Review in 1983, the group needs to be small. “As group size increases, courts become skeptical that the defamation could reasonably be understood to refer to any individual group member. … Reasonable persons do not take literally statements defaming groups of people, and understand such statements only as generalizations or exaggerations.”

The concept has roots in old English law, she noted, which decided the matter in King v. Alme and Nott. “Where a writing … inveighs against mankind in general, or against a particular order of men, as for instance, men of the gown, this is no libel, but it must descend to particulars and individuals to make it a libel,” the ruling said.

It’s unclear how many members belong to the University of Virginia’s chapter of Phi Kappa Psi. Its Web site doesn’t say. But its membership probably numbers in the dozens, if not more, and when the chapter referred on Monday to “damage both to the chapter and its members,” it presumably meant all of the members.

This would likely be considered a large group. And it “might be too large for the defamation-of-a-group theory to apply, especially since the allegation is just about nine members,” wrote the University of California at Los Angeles’s Eugene Volokh in The Post’s Volokh Conspiracy. But as Volokh pointed out, the sheer number of defamatory allegations that now seem untrue are numerous. So even if the frat decides against suing, any number of others in the article could choose otherwise.