The shooter was ID'ed as a suspicious around an hour before the shooting. ABC News is reporting that he didn't even use a ladder to get up to the roof. He climbed up A/C units. Maybe the ladder seen in helicopter images was placed there after the shooting.
He was spotted on the roof by a sniper over twenty minutes prior to the shooting and again reported as suspicious. There is no mention of anyone making contact with him as a result.
It turns out the local cops were not in that building as reported by the head of SS (she got that wrong too). They were in the building right next to it, so despite the building being ID'ed as a threat, nobody secured it. Local cops had two or three sniper teams there. Beyond that, they claim they told SS they only had enough manpower to handle controlling gate access. They were using this building has their base.
Apparently, the gun he had was an AR-15 chambered in 5.56 that he brought in taken apart in a backpack, but all of the images I've seen of him don't include a backpack.
There is mention of a bicycle, but he drove a Hyundai Sonata there. There is an image floating around of a backpack sitting on the ground next to a bicycle, but the shooter isn't in the image. So who knows where that picture came from...
It has already been reported that there was an IED in the car that was hooked up to a remote control he had on the roof. He also stopped at Home Depot that morning and bought a five foot ladder which I assume was in there along with the backpack containing the rifle and likely the range finder he was seen using, and he was able to fit a bike in this Sonata??? He must be an efficient packer.
View: https://www.youtube.com/watch?v=NDufyy6pUoQ