Ranchers in Colorado shot down an unidentified flying object on Christmas Eve, 1947, after having read too much about the Roswell, NM incident in July of the same year. They found an overweight old man slumped over a sleigh that had crashed into the ground, surrounded by the carcasses of nine caribou.

The man's corpse was salvaged and pictures taken. However, by the time the FBI was called in to investigate, the caribou corpses had been eaten by scavengers and the sleigh could not be positively identified as anything more than a "Christmas decoration". The body had disappeared and the entire incident was closed in FBI archives as "common vandalism" and deemed a matter for local authorities.

However, 1948 turned out to be the infamous "Year without a Santa Claus" and it is speculated that the aliens that did indeed crash at Roswell are now responsible for deliveries of presents attributed to "Santa Claus". Given they look much like what people imagine elves to look like (though it's silly - real elves are actually average height but with extra-long fingers and noses), people assume the aliens are "Santa's elves".