Well of course its not the guns fault, however criminals will tend to use the easiest tools to get the job done. This tends to be true even if they are not thinking clearly. Having easy access to these weapons, AR-type weapons and the like, allows for criminals to do more damage and kill more people then if they didn't have access to them to begin with.
RE: Reality Check: Trump Did Not Make It Easier for Severely Mentally Ill People To Buy Guns