Someone local ?.
I had a similar thing, local bushes (within a busy urban area) were strewn with empty cans, focused in quite a specific point. I always wondered who, what, why etc ?
Then one day I saw an old guy wandering along the path, drinking. He saw me coming but still cheerily finished the can off and lobbed it in the bushes. He smiled and said something as I passed. I retorted he was a fkin idiot.