It wasn't because they were hard to steal - they were in an easily breakable glass case - but for the simple reason that the 1m long folios proved too heavy to carry.
In full view of other library users, the thieves abandoned the Audubons on the floor, before fleeing to a getaway car - not a Bullitt-style Ford Mustang, but a Dodge Caravan borrowed from one of the thieves' mothers. The whole thing seemed less like The Thomas Crown Affair and more like a student prank.
Remarkably, that was more or less what it was - albeit one that went far beyond usual frat house antics. Two months later, the FBI arrested Spencer Reinhard, a Transylvania arts student, Eric Borsuk, an accountancy major, Warren Lipka, a football scholar, and Charles Allen, a business major.
"It started out as this weird idea, but in the end, we built up the fantasy so long that we felt if we didn't actually do it, we wouldn't be able to move forward in life," Borsuk, now 33, tells me from the US when I speak to him on the phone.
"So we made leaps in our minds about how easy it would be to get away with it."
All were from comfortable, middle-class backgrounds - which, it seemed, was precisely the problem: their futures felt too secure, a lifetime in suburban America with no chance to make their mark.
But while more conventional rebels without a cause might have joined the Peace Corps, formed a punk band, or taken a gap year, these four decided to become high-end art thieves.
Even for a heavy weed smoker like Lipka - the heist's unlikely slacker-cum-mastermind - it was quite a leap of imagination.
The four certainly made their mark. The theft was headline news across America, as well as earning each of its protagonists seven "gap years" apiece in federal prison.And now, their exploits have been recreated in a critically acclaimed film, American Animals.
The narrative feature debut of British director Bart Layton, who made his name with documentary The Imposter, it splices real interviews with the felons with a re-enactment that sticks as closely as possible to the original story.
"The crime itself seemed so misguided, and these were young, well-educated men with plenty of opportunities," Layton said.
"I wanted to get to grips with the why of it."
Even so, much of it seems barely believable. What sort of amateurs would plan their tactics by watching heist movies like Snatch and Oceans 12?
Why, when arrested, did Lipka have, not just the books by his bed, but also a five-page typed plan for the heist? And why on earth did Eric Borsuk agree to take part, given that he was hoping one day to join the FBI? Was normal life really that boring?
"I think, yes, we all felt that to a certain degree, this was about searching for a life with meaning," Borsuk says. "I grew up in this cloistered, conservative, southern American society, and I found I just didn't agree with it any more. So when the others came to me with this [heist plan], it seemed paradoxically, the perfect proposal."
Indeed, in some ways, it was. The gang got the idea after Reinhard went on a freshman tour of a library, during which the librarian, Betty "BJ" Gooch, mentioned the worth of the 19th-century Audubon folios.
Full of exquisite, life-size drawings, they were one of only 120 sets in existence.Thieves had targeted other sets around the world, yet at the university, the sole security protocol was that visitors to the rare books room had to make an appointment by email with Gooch. Fort Knox it wasn't.
Borrowing colour-coded pseudonyms from Reservoir Dogs, "Mr Green, Mr Yellow, Mr Black and Mr Pink", they set to work, casing the library and studying getaway routes, just as they'd seen in the movies.
Still, while there was no need for Reservoir Dogs-style bloodshed, their nerve failed on their first attempt. Having disguised themselves unconvincingly as whiskery, book-loving pensioners - Lipka's flowing grey beard looked more like a hipster's - they approached the rare books section to find Gooch with a colleague.
They decided to come back the next day when she was alone - and also ditched the eccentric costumes, after wisely deciding they drew attention. (Gooch later said she thought they were drama students fooling around.)
The following morning, the robbery went ahead, Lipka subduing Gooch with a stun-gun, tying her up and gagging her. It is one scene in the film where Layton took liberties, showing a pool of urine appearing across the librarian's trousers.
"It was an invented detail to show the audience how traumatic it was," said Layton, who interviews Gooch in the film.
"I offered her the choice of not having it in, but when she saw it, she said she was happy with it.
"This may sound melodramatic, but I feared I might die that day," Gooch, now 66, says.
"I was also emotionally vulnerable at the time - it was a lot more than I could handle."
Stealing the books, though, was straightforward enough: the hard part was finding a buyer. Lipka, who was already dabbling in petty fraud, claimed to have a criminal contact who introduced him to an underworld "fence", or buyer, in Amsterdam, a major hub for stolen art.
The fence offered to buy the books for a third of their value, but insisted the gang get them authenticated at Christie's first. Foolishly, the gang used the same email address to make the Christie's appointment as for the appointment with Gooch.
It was then only a matter of time before the FBI connected the two, although when armed police finally crashed through their doors, Borsuk actually felt relieved. "We'd realised by then that we weren't going to get existential satisfaction from what we'd done, and we were glad to be no longer looking over our shoulders."
Yet for all the film's forensic investigation of events, it deliberately leaves one question still a mystery. Did Lipka's Dutch "fence" really exist, or did he just make it up, to convince the others to go along with the plot?
Lipka insists it was all true, but Allen, with hindsight, is sceptical, pointing out that Lipka told him he travelled to Amsterdam to meet them on a fake passport - not something an amateur criminal could lay their hands on easily. "At 19, I didn't realise how ridiculous that sounded," Allen adds.
Dick Ellis, a former head of Scotland Yard's arts and antiques squad, also has his doubts. "There is a market for stolen art, but it's usually as collateral between big-time drug barons, and he'd need incredible contacts in the criminal world for anyone to go near him."
Then came prison. Allen says it was a beneficial experience in some ways. "Everything I grew up seeing on TV about prison - the gangs, the drugs - actually happens. But mostly, it's about overcoming boredom and finding ways to be productive."
That, they certainly did. Adding a dubious twist to the tale, the gang credits prison with being the first time they were able to really free themselves from society's expectations - and find their vocation.
Lipka, Allen and Borsuk are all writers, skills honed in prison, while Reinhard has continued his art career, painting a poster for the film.
Might the fact that they are now the stars of their own heist film suggest that crime has paid off - through fame, if not fortune? It is a question about which Gooch is ambivalent.
"It bothers me a little that they will become famous," she says. "I hope now that they'll lead fruitful, productive lives."
Nevertheless, Borsuk insists it is a cautionary tale - and seems to have the fan mail to prove it.
"I get emails from parents who fear their own kids are at risk of getting into trouble," he says. "The parents say: 'we took our kids to the film and it changed their minds'."
