If not for those meddeling patriots alerting a cop that there was a shooter on that roof and that cop alerting that sniper and that sniper blowing yearicks brains out Yearick would have been snuck out of there and Crooks would have been swatted within hours.
Think that over and put the puzzle pieces together.
I'm guessing the ladder was there for him to get onto the roof, not necessarily get off the roof. In fact he probably assumed he would die on the roof.