Intelligence officer Luis Elizondo served as the former director of the Pentagon's Advanced Aerospace Threat Identification Program (AATIP), an initiative launched in 2007 to study reports of UFO encounters. Elizondo departed the Pentagon in 2017; that year, he spoke with reporters at The New York Times, confirming the existence of the shadowy agency and describing its mission.

Now, Elizondo is pulling back the curtain on his tenure with the AATIP, which he left because of a lackluster official response to the agency's findings, and their unwillingness to address potential risks from UFOs, according to the new show "Unidentified: Inside America's UFO Investigation," premiering May 31 on the History Channel at 10 p.m ET/9 p.m. CT. [UFO Watch: 8 Times the Government Looked for Flying Saucers]