That would be my first thought as well. Keep 2, at least, and report the third at worst, so at least they’re aware of activity in the area.
You’re assuming there were only three to begin with! Maybe he kept the non-rusted specimens.
I would report them as they could be important. I would also file a claim to them as lost property. If the owners not found they should be mine.
Of course actually getting them back would be highly unlikely even if the law says they should.