News crews just went inside the home. There were a bunch of passports and fake IDs as well. This definitely was not just a reclusive coupe who got mad.
Neighbor and worker who said he didn't report them also said he saw half dozen middle eastern males in and out of the townhouse in the past week at late hours. Computer records show contact with known terrorists overseas.
This is what I think. My own personal opinion based on the current evidence. Said traveled to Saudi Arabia and made contact with extremists. Married his wife who was trained by them to get him on correct path of Jihad. They planned this for awhile with outside support, explains the money for the materials and weapons and accessories. Fake passports and things go along with who they helped move around with under the radar of the Feds. They chose the party crowd because it was a soft target and a captive group for easy targets. The reason they stayed in the area was to reload and grab the pipe bombs in the home and come back to the scene while cameras and emergency workers and victims were being helped and toss them into the crowd for dramatic effect. Sort of like the way extremists have been known to create an initial attack and then in the chaos after, launch another one much larger to create mass casualties.