Based on Google Earth and police PIO reports, the shooter used a fixed, unsecured ladder likely in the alley, described as a “fire escape”. The ladder in the picture looks a lot like a 24’ extension ladder commonly found on a fire engine. There were video shots of a cop on that roof, and it looked like that ladder was there, IMHO provided by the FD. Just my 2 cents....
That’s no doubt closer to the truth re-the ladder. The aluminum ladder seems to be part of the investigation. Mike Tobin (FOX) notes there is a built-in ladder, called a fire escape, but the building is single story. There is quite a bit of HVAC equipment mounted on the roof so the built in ladder is most likely for maintenance of that. The creep lives in the neighborhood so very likely knew about the access ladder. FWIW a normal fire escape ladder would not be reachable from the ground. The first guy down one swings it to the ground.