I have also heard of a sword handle that was found in roughly the same area. I wouldn't be surprised if the park is full of grave (pun intended) histories that they don't want to talk about. It's part of why the 2015 Howl-O-Scream theme (Unearthed) fit the park so well.
There are some articles from the early 70s out there somewhere about excavations that were made while building the park. For a while, some of the artifacts found were on display at the old Anheuser-Busch hospitality house. I don't really what they were required to do with those things at that time. It would be interesting to have a history of the land before the park existed, especially without having to look too far back on this site.