Very weak evidence - but this must be considered before tossing the idea in the trash.
My question is: How in the world did the guy get 10 long guns up to his room without raising eyebrows ?
From memory: The Tower shooting in Austin, Texas - think that was 32 dead. Mr. Wizard - Can you remember what the guy's motive was ? Yeah - could web-crawl - but lazy today, or more precisely, don't wish to muck wade this early in the week.
Enywhoooz - the possible ISIS link - two major points of the article.
1.) ISIS did release a vid of the Vegas Strip in May of this year - and has, more than once, suggested it as a target.
2.) ISIS, so far, has never made a claim for a terror attack that they were NOT responsible for.
Here's the article, well written, from Allenwest.com
Isis claims responsibility for Vegas massacre — and releases one CHILLING fact
http://www.allenbwest.com/2017/10/02/isis-claims-responsibility-vegas-massacre-releases-one-chilling-fact/
Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...