Or it was a murder weapon.

Seems a lot less likely. She's a well-known actress; I doubt she ever killed anyone, even in self-defense. There just aren't enough murders around here to make it a reasonable guess.

Yeah, don't think it's a given (and you have more context to determine that). It's just what comes to mind when hearing/reading about a buried knife (i.e. something you don't typically bury & could be evidence in a crime case).