On January 7, 1943, Nikola Tesla was found dead in his room at the New Yorker Hotel at 86. His nephew, Sava Kosanović, went to the room the next day, and reportedly claimed that certain key possessions of Tesla’s had been taken—namely, “technical papers” and a black notebook containing notes on some kind of government work.

Tesla was a renowned Serbian-American inventor who created the Tesla coil, engineered the first hydroelectric plant, pioneered the use of the alternating current, and laid the foundation for our modern power grid, among countless other inventions and scientific contributions. Tesla was truly ahead of his time, and quite a few of his ideas—notions that were unfathomable in that day and age—are still being pursued to this day.

According to the FBI’s redacted files on Tesla, made public in 2016, Kosanović indeed went to his uncle’s room to open the safe and retrieve a few things (a book and three photos), though no mention is made of the supposedly missing items. The FBI reported that Kosanović later told Walter Gorsuch, of the Office of Alien Property Custodian (APC), that he had been looking for Tesla’s will. (The APC was in charge of confiscating enemy-owned property during WWI and WWII.)

The FBI’s files clearly express that the U.S. government didn’t trust Tesla’s research in the hands of his nephew, who was the Yugoslavian ambassador to the U.S. The bureau was concerned that he might turn over such coveted information to the “enemy.” So the following day, the APC confiscated all of Tesla’s items, which amounted to “two truckloads”—though it’s worth noting the FBI files state the office didn’t think it even had the legal ability to do so, since Tesla was a naturalized citizen.

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A thermoelectric coil—one of Tesla’s inventions that did come to fruition, 1895.
Roger Viollet//Getty Images

At the time it was rumored that Tesla may have made some incredibly powerful and life-changing discoveries. On September 22, 1940, the New York Times reported that Tesla had created a “death ray” that could melt airplane motors from 250 miles away, called the “teleforce.” Supposedly, this teleforce “would operate through a beam one-hundred-millionth of a square centimeter in diameter, and could be generated from a special plant that would cost no more than $2,000,000 and would take only about three months to construct,” according to the Times. If true, such a weapon would be critical to national security.

Tesla had also worked on trying to beam electricity through the air (this also inspired his teleforce), which would have been a huge breakthrough; in fact, wireless electricity is still a potential technology being explored by the U.S. government and others to this day.

Tesla furthermore thought he could collect and harness what he called “cosmic energy” that he theorized existed in the atmosphere. There’s been a long-running (and debunked) conspiracy theory that Tesla succeeded in creating a way to generate this free, unlimited energy, but that the government suppressed the information as it would have upended the industry and revolutionized society.

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Equipment inside the Wardenclyffe Tower, built by Tesla in 1901 to transmit wireless energy. Shoreham, Long Island, New York State, 1916.
FPG//Getty Images

Soon after the APC collected Tesla’s belongings, an electrical engineer with the National Defense Research Committee (created during WWII as a way for the government to coordinate with scientists for purposes of national defense) by the name of Dr. John G. Trump (yes, of that Trump family—Donald Trump’s uncle) was tasked with investigating Tesla’s papers for anything that might be of importance to the government. Officially, he concluded that Tesla’s papers “did not include new, sound, workable principles or methods” for wireless power. And that may have very well been true—Tesla became increasingly eccentric and obsessive later in life, and his claims could’ve just been wild theories that never came to fruition.

Still, following WWII, the U.S. government renewed its interest in developing beam weapons inspired by Tesla’s research. As described in Margaret Cheney’s biography, Tesla: Man out of Time, in 1945, the Air Technical Service Command at Wright Reid, Ohio, requested photostatic copies of Tesla’s papers on beam weaponry from the Office of Alien Property Custodian. Four months after the APC sent them, the agency requested them again, supposedly having never received them. Two years later, the APC asked for the copies to be returned, and the Air Technical Service Command said they would be, sometime in 1948—but they never were.

It took years and a court hearing for Kosanović to finally receive his uncle’s possessions in 1952. Even then, a good number of Tesla’s belongings were missing—reportedly, his family only received 60 trunks full of his research out of the eighty Tesla had said he’d had.

The U.S. government did keep classified copies of Tesla’s research papers, but the originals are now housed in the archives of the Nikola Tesla Museum in Belgrade, Serbia.

The question remains, though: Did it return all of them?

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Jessica Coulon
Service and News Editor

When she’s not out riding her mountain bike, Jessica is an editor for Popular Mechanics. She was previously an editor for Bicycling magazine.