The music had been going for some time (hour?) according to one of the other threads.
My guess is the plan was for the IED in the apartment to detonate and draw LE/FD/EOD there and give him a few extra minutes.
I think he had bigger plans and the death toll would have been much greater had his conscience not awakened. Waaay late but I think it did. He was/is smart and had a huge and complex plan for a massive death toll, just look at the amount of ammo he purchased. His good kid side just caught up to him to late and didn't save him from the dark side. He is a sick kid that should never see the light of day again but I just can't read him as always and forever evil. He flipped a switch somewhere along the way in his college years. His youth and habits led there but he is truly, as I see it and from what we know at this point--he a good kid that just flipped the F out in the most unimaginable and horrific way. For this guy, I think the death penalty would be his easiest way out. Living with this will eat him alive.