We now know this thanks to the Freedom of Information Act (FOIA), which allows for long-buried files on all sorts of criminal investigations to be declassified and made available to the public. This includes, it turns out, the FBI's brief investigation into the existence of Bigfoot back in the mid-'70s, which is when America's Bigfoot obsession was at its peak.
Earlier today, the FBI Records Vault account casually dropped its 22-page investigation into the possible existence of the infamous Sasquatch. And on Twitter, of all places.
The actual report, which you can read in full here, mostly follows the correspondence between Bigfoot Information Center and Exhibition director Peter Byrne and FBI Agent [REDACTED]. Basically, Byrne had found a hair sample that he believed could be proof of Bigfoot's existence and wanted the FBI's lab to test it.
Even though the FBI pointed out their lab "primarily conducts exams for law enforcement agencies in connection with criminal investigations," they made an exception after several mainstream news outlets had been running stories about the mythological creature.
After several months of follow-ups, the FBI eventually concluded that the "hairs are of deer family origin," and not Bigfoot. Or, at least, that's what it wanted everyone to think.
Anyway, the whole thing really is a brief, fascinating window into an era that had propelled Bigfoot from a fringe conspiracy theory to a (relatively) mainstream pseudoscientific belief. So much so that a federal law enforcement agency elected to weigh in on the matter.