Sad end, but it looks like it was used by someone with a loose sidestand.

I had to remove a cotter pin from one of my bikes this week, a hard bike to work on as it appears to have been assembled by a gorilla - even the head of the cotter pin bulged out. After a week of trying to remove it the usual ways I decided to saw off the head to make it quicker to drill out. The vibration of the sawing actually freed off the pin, as I discovered when I gave it one last chance to come out with a G-clamp.