My great uncle told me about a crash retrieval experience during his time in the military. Could it be legit or BS?

My uncle used to serve in the military around the 70’s/80’s and told me about a pretty interesting experience.

He served for the Bolivian military and was commissioned to stand guard in the Salar de Uyuni desert. He told me that one time a large aircraft fell out of the sky and crashed into that desert. He got called to check at the crash site, but before he could get there the American government was already present and “claimed” the crash site.

My uncle was not allowed to come any closer to the crash site and was only able to vaguely take a look from a distance. He described the ship to have flickering lights of several colors and saw the Americans retrieving some pieces from that ship, alongside some organic material that looked like deceased beings (he never knew if he could consider those things human or not).

Sadly this is all he told me, I don’t know how the rest of the Bolivian military reacted to this incident. Unfortunately I was also too young to ask any more questions that could’ve been of value when he told me this experience.

Does anyone know about any crash reports that happened in the region I mentioned? I’m really curious to hear if there’s anything else out there that has reported this crash as well.