Sorry I can't provide the source for this proof, but I know this to be fact.
This is new news for me, if true. I've love to see a source on that.
I would SUSPECT (intuitively) that people WOULD be swayed SOME by the ready availability of a weapon - but that the effect would NOT be as large as some might think.
But I could be wrong here... especially given that there is SOME ready availability of a weapon for anyone older than 16 who would contemplate attempting such a thing - in the form of automobiles and concrete overpasses.
And of course there are always razor blades and closed-in garages, too.