Experts from a US museum believe it could be one of the oldest examples of advanced surgery. The Museum of Osteology in Oklahoma said the skull is reported to have been that of a man who was injured in battle before undergoing surgery to implant a piece of metal in his head to repair a fracture.
Looks like it covers the damaged part of the skull, for one. If it was for execution it is unlikely it'd just cover that spot. It's not exactly a lot if you're just trying to execute someone. Not that I'd want any amount poured on me.