Nothing is silly.
I don't actually know. I'm currently googling Marine Corps and November13 deaths/murders because the more I think about it the more convinced I'm becoming that the sheath was a 'signature' of sorts. I'll keep looking.
So far, just this, don't see any possible connection but other eyes will know better
Marine Corps says accident took place during range maintenance operation on the base.
eu.usatoday.com
That's just a preliminary report. I've not seen full investigation and it's only a wild wild longshot..
Did he have friends /family in MC?
Did he lose somebody in MC?
He could have done it with any kind of a knife..why the elaborate sheath?