I'd say it would be prudent to take these murderous thugs at their word. FBI already admitted that they just did not listen to, or follow up on these two from Garland Texas, because there were 'so many of them out there now'.
Our government has set the stage, and brought into America a cast of hundreds of thousands of muslims. Somalia, Iraq, Afghanistan, Pakistan and other locations. We already know that thousands are more than willing to travel and kill in the name of their insane religion. NO reason to think they won't make this a daily thing here.