I've heard all kinds of "stories" about this guy and it's tough to tell what is what.
But unless he was literally in contact with them and training with them (or something like that), there's no evidence he did anything but invoke their name.
Being ISIS and using their name as its own form of terrorism are two different things.
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Mac,
There is no evidence just yet saying was this guy mentally disturbed who happened to be Muslim or is this an ISIS led attack...
The former is looking more likely but I think having respect for the dead by not speculating on this before proof...