There is a special place saved in the pantheon of art thieves for those who commit their crimes while displaying almost supernatural feats of athletic prowess.

Thieves who climb up walls, through windows, or prowl around raising nary an alarm get nicknames like “Spideman” and “Ghost.” They have even inspired their own sub-genre of thrillers—think Catherine Zeta Jones’s Cirque de Soleil-worthy contortions to steal a valuable mask in Entrapment.

But it’s Tom Cruise’s vault heist in Mission: Impossible that is the most apt model when it comes to a recent theft of 160 antique books from a warehouse in London.

Late in the night on Jan. 29, three still-unknown thieves drilled through the skylight of a building near Heathrow Airport and rappelled 40 feet to the floor, bypassing the security alarms.

They went straight to six specific crates that contained three dealers’ worth of books that were en route to the California International Antiquarian Book Fair in Oakland.

Over the course of several hours, they unloaded the books they wanted into duffel bags, belayed their loot to the roof, and took off in a waiting van. The haul totaled nearly $2.5 million.

“Behind these books there is a lot of work because we have to search to try to find out where the books are—auction houses, collectors, colleagues—and there’s big research behind these books,” Alessandro Meda Riquier, one of the affected dealers, tells Sky News. “They are not only taking money away from me but also a big part of my job.”

Riquier was the owner of several of the most noteworthy tomes that were taken in the heist. The most expensive book was a second edition of Copernicus’s On the Revolutions of the Heavenly Spheres from 1566 in which the astronomer introduced his revolutionary theory that the sun—not the Earth—is the center of the universe.

That book alone is worth over $250,000. Among the rest of the trove are several rare editions of Dante’s Divine Comedy and a smattering of Galileos, Newtons, and da Vincis, among other titles from the luminaries of the early sciences.

All in all, it is the quantity of books stolen rather than the individual titles that make this heist so significant.

“The books were there for only a short time in that warehouse, and this is a very exotic commodity so this is not something that the average person thinks that they can sell,” Jeremy Norman, a rare book dealer with a specialty in the early sciences, tells The Daily Beast. “I think it’s a real mystery. You really wonder how they knew the stuff was there, and the timing of it, and how they were shipped off, and what the real motivation was.”

Several theories have been offered as to why the thieves went after this quarry. One suggests that this may have been a “made to order” theft, one in which a buyer specifically commissioned the thieves to take these titles.

Similar to fine art, stolen antique books are very difficult to sell on the legitimate market—and thereby net the title’s full value. When a rare book crime becomes known, organizations like the Antiquarian Booksellers Association of America (ABAA) quickly take action to alert their members to the volumes that were stolen so dealers can be on the lookout for anyone trying to offload a tainted treasure.

“If you’re a seller, you’re not going to want to touch something that might remotely be even possibly stolen because you’re going to lose a lot of face with your customer,” Susan Benne, executive director of the ABAA, tells The Daily Beast. She points out that the rare book market deals in a lot of repeat transactions, books that change hands multiple times.

The difficulty of sorting out a stolen book after it has made its way through a few owners ensures that most booksellers are painstakingly principled when it comes to provenance.

“It’s a real hassle to have to go back through the process of dealing with insurance companies, with law enforcement,” Benne says, noting that “above and beyond wanting to do the right thing anyway” dealing with stolen material in the end isn’t worth it for dealers.

While a wealthy collector with a gleam in his eye could have commissioned the theft, the more likely scenario is that it was a crime of opportunity. In this theory, a gang of nefarious local elements had help from someone inside the warehouse’s operation who tipped them off to the presence of the expensive cargo and the exact details of the books’ schedule and location.

The shipment was only being stored for a few days, so the opportunity to take the books, not to mention the ability to quickly pick the correct crates out of a room full of other goods that were left untouched, most likely required some help. As Norman says, “to coordinate such a thing, this is like in a movie, how would you know?”

But if this is what happened, the three felons are most likely sitting somewhere scratching their heads right now trying to figure out how to get rid of their ill-begotten library.

“Maybe it was tempting to professional thieves who didn’t understand that this isn’t going to be something that you can fence like jewelry,” Norman says. “I can tell you it’s not going to affect the prices of books, and it’s going to be really hard for these books to be converted to cash if that’s what they want to do.”

Another member of the community, Chris Marinello, CEO of Art Recovery International, offered The Guardian a more dire warning for what might happen if these thieves find it difficult to cash out.

“The books might then be broken up,” he says. “Some of the illuminated manuscripts and engravings contained therein might be traded in the art market, where many buyers don’t know they were cut out of rare books. It becomes a lot more difficult to trace.”

The antique book community is no stranger to crime, but the London heist broke the previous mold. It’s not uncommon for rare bookstore owners to catch someone slipping a book into their pocket—Norman says he dealt with this occasionally at the store he owned for 30 years. And institutions like libraries that have a permanent collection of treasures are not immune to thefts, whether from outsider thieves or by employees or visiting scholars who are looking to make a few extra bucks on the side.

“I mean the thefts that have been really disruptive and sort of shocking in our world, a lot of them more recently have come from libraries,” Benne says.

As a comparison to the London theft, Norman mentions the 1969 attempt on the Gutenberg Bible at the Widener Library at Harvard.

The amateur thief lowered himself by rope into the room where the Bible was displayed, packed the two volumes up in his backpack, and attempted to scale back up to the roof. Unfortunately, he miscalculated how heavy the tomes actually were—over 60 pounds when carried together—and he fell to the ground. Needless to say, the crime was thwarted.

But incompetence isn’t the only thing that separates the 1969 attempted theft from the 160 books successful stolen in January.

“The books in the Harvard Library were there for years. Everybody knew about them, they weren’t going anywhere, you could target it. That [theft] was daring and it flopped,” Norman says. “[The London theft] took real skill… that’s got to be professionals. So now we’re up against professional thieves, and we could have more trouble than we used to have in the past.”