This is a second hand story.
I heard it from an old friend while I was in high school, which was 1960 through 1964.
He had graduated from UCLA engineering school, and was on vacation in, as I recall, Mexicali, Mexico, with a friend.
The year was schetchy, but I know he said it was after the war had ended, and before 1958.
Over the city plaza, a large disk, perhaps 200' across just appeared and hovered.
He and the friend noticed first that the town's people were jabbering and pointing in awe at this thing above them.
The disk was sivery, with noticable portholes, and it perhaps 200' to 500' above the plaza.
He was very impressed by it, for it darted over here to the left, then to the right, then in a moment, it dashed completely out of sight.
As a recent grad from engineering school, he knew that nothing he had ever seen or studied could possibly withstand that kind of forces of acceleration and maneuvering agility.
He concluded that it therefor must be extraterrestrial.
He was guarded as he told us, for he didn't share the account for concern that others would think him to be crazy.