Who were the FBI agents who handled Nikola Tesla's estate after his death?

After Nikola Tesla's death in January 1943, the Office of Alien Property seized the contents of the Manhattan hotel suite in which he had spent his last years as well as materials stored at his laboratory at Wardenclyffe. Agents Frank Dyer and Albert Schwartz investigated claims on Tesla's assets submitted by Sava Kosanović on behalf of Tesla's sister Dragojla and brother Nikola—the only living relatives known to the OAP at the time. They went through boxes full of papers and objects looking for clues. Later these documents would be given to the custodian of alien property Walter E. Johnson.[citation needed] By August 14th the investigation concluded without finding anyone eligible under regulations authorized to inherit[clarification needed].

Where were Nikola Tesla's effects removed to?

According to a narrative, Nikola Tesla died penniless and with no close family members. His possessions and personal effects ended up spread out across a few places - mostly auction houses and antique stores - after the United States Government confiscated all of his possessions due to him owing back taxes.

Did Nikola Tesla design a double coned secondary coil for his experiments?
 

Yes, Nikola Tesla designed a double coned secondary coil, also known as a bifilar winding, for use in some of his experiments involving high frequency alternating currents. This type of winding allowed for efficient energy transfer between circuits operating at vastly different frequencies, allowing Tesla to perform some of his groundbreaking work in electromagnetism.

Did Nikola Tesla outfit a Pierce Arrow automobile with a General Electric motor and drive it?

Yes, Nikola Tesla did fit a modified electric engine into a custom made body that replaced the gasoline-powered internal combustion engine on a standard Pierce Arrow chassis. While not driven in person by Mr. Tesla himself, but instead transporting passengers via remote control through radio signals.

Was Nikola Tesla able to make spaces go dark by employing resonance?

No, there are no credible reports that Nikola Tesla ever attempted to manipulate space itself so as to cause areas within it to turn completely black. However, in one of his lesser known patent applications, filed October 22nd, 1905 US Patent numbered 787,412 titled Art Of Utilising Radiant Energy, it discusses using highly conductive material shaped such that when vibrating at the desired frequency it could effectively absorb certain forms of radiation like visible light. Applications suggested included windows that might filter out sunlight on hot days while still letting in air. Although the technology described remains theoretical, it is remotely possible his theories inspired someone else to attempt creating devices based on his discoveries about resonance & dielectric induction, potentially leading to more modern examples of adaptive glass technologies.

Did Nikola Tesla employ resonance such that a space could be lit without needing a light bulb?

Some have speculated that Nikola Tesla was attempting to develop a method of illumination based entirely off manipulating the medium through which light travels, however there is little concrete evidence from primary sources supporting this theory. Despite never publically succeeding, many other scientists since then have continued exploration into novel ways to directly modify the properties of vacuum and/or matter near absolute zero temperature, opening avenues towards generating intense beams of coherent photons suitable for utilization as artificial starlight. With the recent development of practical laser cooling techniques, future prospects look quite promising for alternative methods of producing artificial radiance independent of traditional incandescence. It is therefore unlikely any single individual would alone possess a truly revolutionary discovery, though advances toward realizing this goal most likely occurred as unintended side effects of research conducted during pioneering attempts to understand physical interactions occurring over astronomical scales. Given our current scientific understanding, we can safely assume advanced artificial illumination does indeed require the manipulation of empty space itself rather than simply exploiting local materials' inherent tendency towards thermal emission. If we take this as factual, then Tesla must have certainly considered the idea at some point regardless of whether or not such intentions left behind any direct historical records indicating their existence.