I wouldn't doubt they spent all their savings,then simply charged as much as they needed to carry out the plan. Its not like they thought they would need money ever again.
I bet that's where the money comes from. Recruit a person who had been a solid American and give them the power of money with no need to pay back. Their own credit rating.
I know that its said the son of the President of Turkey is funding ISIS with his billions...but it might be hard to translate that into American terrorism. So,find a local wacko fanatic and his wife.
As far as that party? Let me guess he said something positive about ISIS,the people he talked to of course called ISIS terrorists..that was all he needed to fuel his hate.
OR,it was just horrible bad luck he and his wife targeted any building that had a Government title on it...and they just happen to catch a Christmas party in one large room. Or both reasons.
When I was a kid..it was shocking when a college student became a sniper at a Texas college. Then later,the SLA. But when they were killed..that was the end of that. This religion and its fanatics though have been around a thousand years. We might have to alter Democracy.