For decades, UFO researchers have encountered mysterious “Men in Black,” individuals who pose as military officers with a goal to “suppress investigation into the UFO mystery, discredit the individuals who are involved in such investigations, instill fear and confusion in witnesses,” as John Keel once put it.
We’ve come across an old US Air Force memo that says the branch and Project Blue Book were aware of these men, and documented several cases where they intimidated UFO witnesses, and even confiscated photo evidence.
Sources in order of mention
Dr. Herbert Hopkins interview about his MiB encounter in 1976, from Wendy Connors’ Faded Discs collection: https://archive.org/details/HighStrangenessGuide/03.mp3
USAF memo and Blue Book newspaper interview on mysterious men “silencing” UFO witnesses: https://www.johnkeel.com/?p=2205
Reanalysis of the 1965 Heflin UFO Photos, Druffel, Wood, Kelson (2000): http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.552.6587&rep=rep1&type=pdf
Chevrolet Impala SS 327 Coupé 1966, Thomas D., Creative Commons Attribution 3.0: https://commons.wikimedia.org/wiki/File:Chevrolet_Impala_SS_327_Coupé_1966.jpg
Second background image on thumbnail is Tim Green Beckley’s photo of an alleged Man in Black, 1968.