Hoax
Yes, a hoax, perpetrated by the muzzies themselves to garner sympathy for their "cause" and an attempt to sway public opinion. After all, in most of the public's minds, who else but radical right wing Republican Trump supporters would do such a thing?
I guarantee, if a massacre were actually planned by someone other than the followers of Mad Mo, no one would know about the plot until they read of it in the paper the day after.